Pressure Conversion Calculator
Convert between 33+ pressure units instantly. Real-time results for Pascal, PSI, Bar, Atmosphere, Torr, and more.
Quick Info
• 1 atm = 101,325 Pa
• 1 bar = 100,000 Pa
• 1 psi = 6,894.76 Pa
• 1 Torr = 133.322 Pa
Pa
Pascal
100,000
SI base unit
kPa
Kilopascal
100
1000 Pascals
MPa
Megapascal
0.10000000
Million Pascals
GPa
Gigapascal
1.000000e-4
Billion Pascals
hPa
Hectopascal
1,000
Weather reports
mbar
Millibar
1,000
Equal to hPa
bar
Bar
1
100,000 Pascals
psi
Pound per Square Inch
14.503774
Pounds-force per square inch
psf
Pound per Square Foot
2,088.54
Pounds-force per square foot
ksi
Kilopound per Square Inch
0.01450377
1000 psi
ozf/in²
Ounce-force per Square Inch
232.060387
1/16 of psi
atm
Standard Atmosphere
0.98692327
Sea level pressure
at
Technical Atmosphere
1.019716
kgf/cm²
Torr
Torr
750.061683
1/760 of atm
mmHg
Millimeter of Mercury
750.061576
0°C mercury column
cmHg
Centimeter of Mercury
75.006158
0°C mercury column
inHg
Inch of Mercury
29.52998
32°F mercury column
inHg @60°F
Inch of Mercury (60°F)
29.613397
60°F mercury column
mmH₂O
Millimeter of Water
10,197.16
4°C water column
cmH₂O
Centimeter of Water
1,019.72
4°C water column
mH₂O
Meter of Water
10.197162
4°C water column
inH₂O
Inch of Water
401.474213
4°C water column
ftH₂O
Foot of Water
33.456229
4°C water column
inH₂O @60°F
Inch of Water (60°F)
401.859807
60°F water column
ftH₂O @60°F
Foot of Water (60°F)
33.488317
60°F water column
N/m²
Newton per Square Meter
100,000
Same as Pascal
N/cm²
Newton per Square Centimeter
10
10,000 Pascals
N/mm²
Newton per Square Millimeter
0.10000000
1 MPa
kN/m²
Kilonewton per Square Meter
100
1 kPa
kgf/cm²
Kilogram-force per Square Centimeter
1.019716
Technical atmosphere
kgf/m²
Kilogram-force per Square Meter
10,197.16
Gravitational unit
kgf/mm²
Kilogram-force per Square Millimeter
0.01019716
High pressure
dyn/cm²
Dyne per Square Centimeter
1.0000e+6
CGS unit (barye)
Why Pressure Conversion Matters
Have you ever looked at a tire pressure gauge showing "32 PSI" and wondered what that means in bar or kilopascals? Or needed to convert atmospheric pressure from weather reports into units your HVAC system uses? Pressure conversion is one of the most common yet frustrating challenges across dozens of industries, from automotive maintenance to scientific research, meteorology to engineering design.
The fundamental problem is that different countries, industries, and applications use vastly different pressure measurement systems. Engineers in Europe work with bars and pascals (SI units), while American technicians use PSI (pounds per square inch). Meteorologists report atmospheric pressure in millibars or inches of mercury, scientists measure vacuum pressure in torr, and hydraulic systems often specify pressure in kilopascals or megapascals. Without quick, accurate conversion, critical decisions about equipment safety, process control, and system design become unnecessarily complicated.
Who Needs Pressure Conversion?
Professional Applications:
- • Mechanical Engineers: Hydraulic system design and troubleshooting
- • HVAC Technicians: Refrigerant pressure specifications and diagnostics
- • Automotive Professionals: Tire pressure, turbocharger boost, fuel injection systems
- • Chemical Engineers: Process control and reactor pressure monitoring
- • Meteorologists: Atmospheric pressure analysis and weather prediction
Everyday Users:
- • Car Owners: Understanding tire pressure recommendations across regions
- • DIY Enthusiasts: Air compressor settings for tools and equipment
- • Students: Science homework and laboratory calculations
- • Homeowners: Water pressure troubleshooting and well pump settings
- • Scuba Divers: Tank pressure and depth pressure calculations
What makes pressure conversion particularly challenging is the sheer number of measurement systems in use. Unlike length or weight, which typically use just a few common units, pressure has over 30 actively used units globally. Each unit originated from different scientific traditions, industrial needs, or measurement technologies. Pascal (Pa) comes from SI physics, PSI emerged from British imperial engineering, bar was adopted for its convenient scale in industrial applications, torr honors the inventor of the barometer, and atmospheric pressure (atm) represents average sea-level conditions.
This calculator solves the conversion problem instantly and accurately. Instead of memorizing dozens of conversion factors or searching through reference tables, you simply enter a pressure value in any unit and immediately see equivalent values in all 33+ supported units. Whether you're converting tire pressure from bar to PSI before a road trip, translating vacuum specifications from torr to pascals for laboratory equipment, or checking weather pressure from millibars to inches of mercury, this tool handles every scenario with precision and speed.
What You'll Learn in This Guide
- How pressure conversion works — The mathematics and logic behind converting between measurement systems
- Real-world applications — Where pressure conversion matters in professional work and daily life
- Industry-specific terminology — Understanding gauge pressure, absolute pressure, differential pressure, and more
- Expert conversion techniques — Pro tips for accuracy, verification, and avoiding common mistakes
- Practical formulas and examples — Step-by-step calculations you can replicate manually if needed
The Basic Concept
Pressure is fundamentally the measurement of force distributed over an area. Imagine pushing on a surface with your hand — the pressure depends on both how hard you push (force) and how large the surface area is. Push the same force on a smaller area, and the pressure increases. This is why a sharp knife cuts better than a dull one: the force is concentrated on a tiny edge area, creating enormous pressure.
Mathematically, pressure equals force divided by area: P = F / A. In the International System (SI), force is measured in newtons (N) and area in square meters (m²), giving pressure in pascals (Pa). One pascal equals one newton per square meter. However, a pascal is quite small for most practical applications, so we often use kilopascals (1 kPa = 1,000 Pa), megapascals (1 MPa = 1,000,000 Pa), or bars (1 bar = 100,000 Pa).
Pressure conversion exists because different measurement systems define force and area units differently. The imperial system uses pounds-force and square inches, creating PSI (pounds per square inch). Atmospheric science historically used mercury column height, creating torr and mmHg. Each system is valid within its context, but converting between them requires precise mathematical relationships that account for the different force and area definitions.
The Mathematics of Conversion
All pressure conversions use a base unit strategy. This calculator uses the pascal (Pa) as the universal reference point because it's the SI standard unit. Every other pressure unit has a fixed conversion factor to pascals. To convert from Unit A to Unit B, we take a two-step approach:
Step 1: Convert from Unit A to Pascals
Pascals = ValueA × Conversion FactorA→Pa
Step 2: Convert from Pascals to Unit B
ValueB = Pascals ÷ Conversion FactorB→Pa
Why this works: Since every unit has a fixed relationship to the pascal, converting through pascals as an intermediate step guarantees consistency. This approach also simplifies the math — instead of needing conversion factors between every possible pair of units (which would require hundreds of factors), we only need one conversion factor per unit to/from pascals.
Key Conversion Factors to Pascals:
• 1 bar = 100,000 Pa (exactly)
• 1 PSI = 6,894.757 Pa
• 1 atm = 101,325 Pa (standard)
• 1 torr = 133.322 Pa
• 1 mmHg = 133.322 Pa (at 0°C)
• 1 inH&sub2;O = 249.089 Pa (at 4°C)
Step-by-Step Conversion Walkthrough
Let's convert a common tire pressure specification: 2.5 bar to PSI. This is a real-world scenario for European car owners traveling to the United States.
Step 1: Identify the conversion factors
From our reference table:
• 1 bar = 100,000 Pa
• 1 PSI = 6,894.757 Pa
Step 2: Convert bar to pascals
Pascals = 2.5 bar × 100,000 Pa/bar
Pascals = 250,000 Pa
Step 3: Convert pascals to PSI
PSI = 250,000 Pa ÷ 6,894.757 Pa/PSI
PSI = 36.26 PSI
Step 4: Verify the result
Result: 2.5 bar = 36.26 PSI
Sanity check: We know 1 bar ≈ 14.5 PSI (rough approximation). So 2.5 bar should be around 36-37 PSI. Our calculated 36.26 PSI is correct!
More Conversion Examples
Example 2: Scientific Vacuum Pressure
Convert 10 torr to pascals
10 torr × 133.322 Pa/torr = 1,333.22 Pa or 1.333 kPa
Used in vacuum chamber operations and laboratory equipment specifications.
Example 3: Atmospheric Pressure Conversion
Convert 30.15 inHg (weather report) to millibars
Step 1: 30.15 inHg × 3,386.389 Pa/inHg = 102,099.43 Pa
Step 2: 102,099.43 Pa ÷ 100 = 1,020.99 mbar
Meteorologists often report in millibars (mb) or hectopascals (hPa), which are equivalent.
Example 4: Hydraulic System Pressure
Convert 3,000 PSI to MPa (megapascals)
Step 1: 3,000 PSI × 6,894.757 Pa/PSI = 20,684,271 Pa
Step 2: 20,684,271 Pa ÷ 1,000,000 = 20.68 MPa
High-pressure hydraulic systems often specify pressure in MPa for cleaner numbers.
Automotive Industry
Tire pressure specifications vary globally — European manufacturers specify bar (typically 2.0-2.5 bar), while American specifications use PSI (28-35 PSI). Accurate conversion prevents under-inflation (poor fuel economy, tire wear) or over-inflation (reduced traction, harsh ride). Turbocharger boost pressure, fuel injection pressure, and brake hydraulic pressure also require conversion when working with imported vehicles or international service manuals.
HVAC Systems
Refrigerant pressure-temperature charts use different units depending on equipment origin. American systems typically use PSI gauge pressure, European systems use bar, and technical specifications often reference absolute pressure in kPa or MPa. HVAC technicians must convert accurately to diagnose refrigerant charge levels, compressor performance, and system efficiency. Incorrect pressure readings from unit confusion can lead to misdiagnosis and equipment damage.
Scientific Research
Laboratory equipment specifications span multiple pressure systems. Vacuum pumps specify ultimate pressure in torr or millibar, gas cylinders list pressure in bar or PSI, and scientific instruments report in pascals or atmospheres. Researchers collaborating internationally must convert pressure data accurately for reproducibility. Gas chromatography, mass spectrometry, and material testing all require precise pressure control with units varying by equipment manufacturer and regional standards.
Meteorology
Weather reports use different atmospheric pressure units by region. United States weather stations report inches of mercury (inHg), European forecasts use hectopascals (hPa) or millibars (mb), and aviation uses hectopascals for altimeter settings. Understanding these conversions helps interpret weather patterns, predict storms (low pressure systems), and adjust barometric altimeters for accurate elevation readings in aviation and outdoor activities.
Hydraulic Engineering
Industrial hydraulic systems operate at extreme pressures requiring precise unit conversion. Construction equipment hydraulics range from 2,000-5,000 PSI, while waterjet cutting systems exceed 60,000 PSI (over 400 MPa). Engineers must convert between MPa, bar, and PSI when specifying components, calculating cylinder forces, and designing pressure relief valves. System safety depends on accurate pressure specifications — unit confusion can result in catastrophic equipment failure.
Scuba Diving
Dive tank pressure varies by region — metric systems use bar (typically 200-300 bar fill pressure), while imperial uses PSI (3,000-4,500 PSI). Divers traveling internationally must convert to ensure adequate air supply planning. Understanding atmospheric pressure in feet of seawater (FSW) or meters of seawater (MSW) is critical for decompression calculations and nitrogen absorption planning during deep dives.
Home Improvement
Air compressor specifications for power tools range from 90-150 PSI, but imported European compressors specify bar. Water pressure for residential plumbing typically ranges 40-80 PSI (2.8-5.5 bar), and well pump settings require conversion between systems. Power washers, paint sprayers, and pneumatic nailers all have minimum pressure requirements that must be converted when using equipment from different regions or reading international instruction manuals.
Education & Training
Physics and chemistry students must convert pressure units for homework problems, laboratory reports, and standardized tests. Textbooks from different countries use varied units — American texts favor PSI and atm, European texts use Pa and bar, and scientific papers use SI units. Understanding conversion builds foundational skills for STEM careers and helps students verify answers across different resource materials and online calculators.
Absolute Pressure
Total pressure measured relative to a perfect vacuum (zero pressure). Includes atmospheric pressure plus gauge pressure. Critical for scientific calculations, gas laws, and thermodynamics. Symbol: Pabs. Formula: Pabs = Pgauge + Patmospheric
Gauge Pressure
Pressure measured relative to ambient atmospheric pressure. Most pressure gauges display gauge pressure, including tire pressure gauges, hydraulic gauges, and air compressor indicators. Zero gauge pressure means pressure equals atmospheric pressure (typically 14.7 PSI or 101.3 kPa at sea level).
Differential Pressure
Pressure difference between two points in a system. Used extensively in fluid flow measurement, filter monitoring (pressure drop), and HVAC systems (static pressure across ductwork). Symbol: ΔP. Common units: inches of water column (inH&sub2;O), pascals, or PSI.
Vacuum Pressure
Pressure below atmospheric pressure. Often expressed as negative gauge pressure or as absolute pressure below 101.3 kPa. Common in scientific equipment, industrial processes, and packaging. Measured in torr, millibar, inches of mercury vacuum, or pascals absolute (Pa abs).
Pascal (Pa)
SI unit of pressure equal to one newton per square meter (N/m²). Named after Blaise Pascal. Very small unit in practical terms; typically use kilopascals (kPa = 1,000 Pa) or megapascals (MPa = 1,000,000 Pa). Standard atmospheric pressure = 101,325 Pa or 101.325 kPa.
Bar
Metric pressure unit approximately equal to atmospheric pressure. Exactly 100,000 Pa or 100 kPa. Common in European industry, automotive specifications, and weather forecasting. Millibar (mbar = 0.001 bar) frequently used in meteorology and is equivalent to hectopascal (hPa).
PSI (Pounds per Square Inch)
Imperial/US customary unit measuring force in pounds-force distributed over one square inch area. Standard in American engineering, automotive industry, and compressed air systems. PSIG denotes gauge pressure; PSIA denotes absolute pressure. 1 PSI = 6,894.757 Pa.
Atmosphere (atm)
Standard atmospheric pressure at sea level, exactly defined as 101,325 Pa. Used in chemistry, physics, and diving calculations. Convenient reference unit because it represents typical Earth surface conditions. One atmosphere supports a 760 mm mercury column.
Torr
Pressure unit equal to 1/760 of standard atmosphere. Named after Evangelista Torricelli, inventor of the barometer. Common in vacuum technology and scientific applications. Very close to millimeters of mercury (mmHg), but torr is defined more precisely. 1 torr = 133.322 Pa.
Millimeters of Mercury (mmHg)
Pressure unit based on mercury column height at 0°C under standard gravity. Traditional unit in medicine (blood pressure), meteorology, and vacuum measurements. Approximately equal to torr. Standard atmosphere = 760 mmHg. Also called "millimeters of mercury column."
Inches of Mercury (inHg)
Imperial pressure unit based on mercury column height. Standard in US weather reporting and aviation altimeter settings. One atmosphere = approximately 29.92 inHg at sea level. Used for barometric pressure in weather forecasts and high-accuracy pressure measurement.
Inches of Water Column (inH&sub2;O)
Low-pressure measurement unit based on water column height at specific temperature (usually 4°C or 60°F). Common in HVAC ductwork static pressure, differential pressure, and gas appliance pressure specifications. Much smaller than inHg: 1 inH&sub2;O ≈ 0.0361 PSI or 249 Pa.
Kilopascal (kPa)
1,000 pascals. Convenient SI unit for everyday pressure applications. Atmospheric pressure ≈ 101.3 kPa. Common in automotive tire pressure specifications outside the US, industrial process control, and engineering calculations. Bridges the gap between small Pa values and large MPa values.
Megapascal (MPa)
1,000,000 pascals or 1,000 kPa. Used for high-pressure applications like hydraulic systems, material strength testing, and industrial processing. Convenient for large pressures: 1 MPa ≈ 145 PSI or 10 bar. Common in structural engineering and mechanical design specifications.
Standard Temperature and Pressure (STP)
Reference conditions for gas measurements: 0°C (273.15 K) and 100 kPa (or sometimes 101.325 kPa = 1 atm). Used in chemistry and physics for gas volume calculations and comparisons. Different organizations define STP slightly differently, so always verify which standard applies.
Quick Reference: Pressure Relationships
Common Equivalents:
- • 1 atm = 101.325 kPa
- • 1 atm = 14.696 PSI
- • 1 atm = 1.01325 bar
- • 1 atm = 760 torr
- • 1 atm = 760 mmHg
Quick Conversions:
- • 1 bar = 14.5 PSI
- • 1 bar = 100 kPa
- • 1 PSI = 6.895 kPa
- • 1 PSI = 51.715 torr
- • 1 PSI = 2.036 inHg
Low Pressure:
- • 1 inH&sub2;O = 249 Pa
- • 1 mmH&sub2;O = 9.807 Pa
- • 1 mbar = 100 Pa
- • 1 mbar = 0.75 torr
- • 1 torr = 1.333 mbar
Professional Tips for Accurate Conversions
1. Verify Gauge vs. Absolute Pressure
Always confirm whether specifications use gauge (PSIG, barg) or absolute (PSIA, bara) pressure. Most automotive and industrial gauges show gauge pressure, but thermodynamic calculations require absolute pressure. Add atmospheric pressure (14.7 PSI or 101.3 kPa) to gauge readings when absolute pressure is needed.
2. Account for Temperature Effects
Water and mercury column pressure measurements vary with temperature. Inches of water at 60°F differs from 4°C by about 0.5%. For precision work, use temperature-specific conversion factors. Most calculators assume standard temperatures (0°C for mercury, 4°C for water).
3. Use Appropriate Precision
Match decimal places to your measurement accuracy. Tire pressure gauges accurate to ±0.5 PSI don't justify conversions to five decimal places. For scientific work, carry one extra significant figure during calculations, then round the final result appropriately.
4. Double-Check Unit Labels
Pressure gauges and specifications sometimes omit or confuse units. "30" could mean 30 PSI, 30 kPa, or 30 inHg depending on context. Always verify units through equipment documentation, industry standards, or reasonable value ranges. A car tire at "2.5" is likely bar, not PSI (which would be dangerously low).
5. Cross-Verify Critical Calculations
For safety-critical applications (pressure vessel design, scuba tank filling, medical equipment), independently verify conversions using multiple sources or manual calculations. Decimal point errors or unit confusion in high-pressure systems can cause catastrophic failures.
6. Understand Regional Standards
Europe predominantly uses bar and kPa, North America uses PSI, and scientific contexts use pascals. When working internationally, confirm which system applies. Equipment labeled for one market may have different pressure ratings than specifications for another market.
7. Keep Conversion Reference Handy
Memorize key relationships for field work: 1 bar ≈ 14.5 PSI, 1 atm ≈ 14.7 PSI, 1 bar = 100 kPa. These approximations enable quick mental verification. Detailed conversions should use precise factors, but rough estimates catch major errors immediately.
8. Consider Altitude Effects
Atmospheric pressure decreases approximately 1 inHg per 1,000 feet of elevation gain. At 5,000 feet, atmospheric pressure is about 12.2 PSI (not 14.7 PSI). This affects gauge-to-absolute conversions and can impact equipment performance specifications rated at sea level.
9. Document Your Conversions
For engineering projects and compliance work, record the original value, conversion factor used, and final result with units clearly labeled. This creates an audit trail and helps troubleshoot discrepancies. Include date and source for conversion factors in formal documentation.
10. Use Digital Tools Wisely
Online calculators are convenient but verify they use correct conversion factors. Some calculators use rounded factors (1 PSI = 6.9 kPa instead of 6.894757 kPa), introducing small errors that compound in multi-step calculations. Premium engineering calculators provide full precision.
Common Conversion Mistakes to Avoid
Confusing Gauge and Absolute Pressure
The Error: Using gauge pressure (PSIG) in thermodynamic formulas that require absolute pressure (PSIA), or vice versa.
Why It Happens: Many pressure gauges don't explicitly label gauge vs. absolute. Engineers assume one system when specifications use another.
Prevention: Look for PSIG/PSIA suffixes. When in doubt, most industrial gauges show gauge pressure. Gas law calculations (PV=nRT) always need absolute pressure.
Decimal Point Placement Errors
The Error: Misplacing decimals when manually converting (e.g., converting 2.5 bar as 25,000 Pa instead of 250,000 Pa).
Why It Happens: Conversion factors involve multiple zeros (1 bar = 100,000 Pa). Mental math errors occur when tracking decimal places.
Prevention: Write conversion factors in scientific notation (1 bar = 1 × 10&sup5; Pa). Use digital calculators for multi-zero conversions. Perform reasonableness checks.
Mixing Torr and mmHg Interchangeably
The Error: Assuming torr and mmHg are exactly identical for all calculations.
Why It Happens: They're extremely close (differ by <0.000015%), leading to casual interchangeability in many contexts.
Prevention: For high-precision scientific work, use the specific unit requested. Torr is defined exactly as 1/760 atm; mmHg depends on mercury density and gravity, which vary slightly with temperature and location.
Ignoring Temperature-Dependent Units
The Error: Using inches of water column conversions without checking reference temperature (4°C vs. 60°F vs. 68°F).
Why It Happens: Water density changes with temperature. Conversion factors vary: 1 inH&sub2;O at 4°C = 249.089 Pa; at 60°F = 248.843 Pa.
Prevention: Check HVAC and low-pressure specifications for temperature standards. When precision matters, use the temperature-specific conversion. For non-critical work, 4°C is common standard.
Using Rounded Conversion Factors
The Error: Applying quick approximations (1 bar = 15 PSI instead of 14.504 PSI) for precision-sensitive applications.
Why It Happens: Rounded factors are easier to remember and faster for mental math. Acceptable for estimates but accumulate error in exact work.
Prevention: Use full-precision factors (1 bar = 14.503773773 PSI) for engineering calculations, technical reports, and equipment specifications. Round only final results, not intermediate steps.
Not Verifying Unit Context
The Error: Accepting pressure values without considering if they make physical sense for the application.
Why It Happens: Blindly trusting calculator outputs without sanity checking. Unit typos or data entry errors go unnoticed.
Prevention: Know typical pressure ranges: car tires 30-35 PSI, vacuum 0-760 torr below atmosphere, hydraulics 500-5,000 PSI, atmospheric 28-31 inHg. Results far outside expected ranges warrant double-checking.
Forgetting Vacuum Pressure Sign Convention
The Error: Treating vacuum pressure as positive gauge pressure or incorrectly converting between vacuum inches Hg and absolute pressure.
Why It Happens: Vacuum gauges may show positive numbers representing pressure below atmosphere (e.g., "25 inHg vacuum"). Converting this requires subtracting from atmospheric pressure.
Prevention: Absolute pressure = Atmospheric pressure - Vacuum gauge reading. A gauge showing 25 inHg vacuum equals 29.92 - 25 = 4.92 inHg absolute, or about 16.7 kPa absolute.
Accuracy, Limitations & When to Consult Professionals
Calculator Accuracy
This calculator uses internationally recognized conversion factors from NIST (National Institute of Standards and Technology) and ISO standards. Mathematical precision is maintained to 6-10 decimal places for scientific applications. However, conversion accuracy exceeds measurement accuracy in most practical scenarios. Your pressure gauge typically has ±1-2% error, making ultra-precise conversions unnecessary for everyday use.
Known Limitations
- • Temperature assumptions: Mercury and water column conversions assume standard temperatures unless specified. Actual pressure may vary ±0.1-0.5% with temperature.
- • Gravity variations: Column-based units (mmHg, inH&sub2;O) technically depend on local gravity. Standard gravity (9.80665 m/s²) is assumed.
- • No correction for compressibility: Assumes ideal gas behavior. Real gases at extreme pressures (>100 bar) may deviate slightly from ideal conversions.
- • Unit ambiguity resolution: When multiple temperature standards exist (inH&sub2;O at 4°C, 60°F, 68°F), calculator uses most common industrial standard.
When to Seek Professional Verification
- • Safety-critical systems: Pressure vessel design, medical gas systems, aircraft pressurization, scuba equipment — require licensed engineers.
- • Regulatory compliance: Building codes, ASME standards, FDA regulations may mandate specific calculation methods and verification by qualified professionals.
- • High-stakes decisions: Equipment purchases, legal disputes, insurance claims benefit from independent professional validation.
- • Extreme conditions: Cryogenic pressures, ultra-high vacuum (<10⁻⁶ torr), or pressures >10,000 PSI may require specialized conversion considerations.
- • Calibration and metrology: Pressure gauge calibration and standards traceability should involve accredited calibration laboratories with NIST-traceable references.
Key Advantages
Instant Time Savings
Manual conversion requires finding conversion factors, performing multiplication/division, and managing decimal places. Digital calculators complete 33+ conversions in milliseconds versus 5-10 minutes per conversion manually. For professionals making dozens of conversions daily, this saves hours per week.
Error Elimination
Human calculation errors — misplaced decimals, wrong conversion factors, calculator typos — are eliminated. Pressure conversion calculators use verified, hard-coded factors that don't change. Reduces engineering rework, equipment sizing mistakes, and safety incidents from incorrect pressure specifications.
Comprehensive Unit Coverage
Instantly converts to 33+ units across SI, imperial, atmospheric, column, and specialized systems. Eliminates need for multiple conversion tables or references. Particularly valuable for international collaboration where different teams use different pressure standards.
Mobile Accessibility
Available anywhere with internet access — job sites, laboratories, service calls, or while traveling. No need to carry conversion charts or specialized calculators. Responsive design works on phones, tablets, and desktops for field technicians and office engineers alike.
Learning Tool
Seeing all 33 units simultaneously builds intuition for pressure relationships. Students and trainees develop better understanding of unit scales (PSI vs. kPa vs. bar) through repeated exposure. Educational value extends beyond simple conversion to deeper comprehension of pressure measurement systems.
Zero Cost
Free web-based calculators eliminate the need for expensive engineering software subscriptions or dedicated hardware calculators. Enterprise teams can standardize on the same calculator without licensing costs. Accessible to students, hobbyists, and professionals equally.
Real-Time Feedback
Interactive calculators update instantly as you type, enabling rapid exploration of "what-if" scenarios. Compare multiple pressure specifications simultaneously. Immediate visual feedback helps catch input errors before they propagate into downstream calculations.
Documentation Support
Copy-paste results directly into reports, specifications, and spreadsheets. Maintains precision through digital transfer versus manual transcription from reference tables. Reduces transcription errors in technical documentation and engineering calculations.
Important Limitations
Requires Internet Connection
Web-based calculators need internet access. Field work in remote locations without connectivity requires offline alternatives (mobile apps, programmed calculators, or memorized conversion factors). Consider downloading offline conversion tools for reliability-critical field applications.
Doesn't Replace Conceptual Understanding
Calculators perform math but don't teach why conversions work or when to apply them. Engineers still need to understand gauge vs. absolute pressure, temperature effects, and application context. Over-reliance on calculators without foundational knowledge leads to incorrect unit selection and misinterpretation of results.
Limited Context Awareness
Cannot determine if gauge or absolute pressure is appropriate for your specific application. Doesn't account for special circumstances like high altitude (reduced atmospheric pressure) or temperature-specific column measurements. User must apply engineering judgment to select correct units and interpret results.
Not Suitable for Safety-Critical Final Verification
While highly accurate, online calculators shouldn't be sole verification for life-safety systems (pressure vessel design, medical equipment, aircraft systems). Professional engineering calculations require licensed engineers, code-compliant methods, and formal documentation. Use calculators for preliminary work, but safety-critical applications need professional verification.
No Audit Trail or Documentation
Web calculators don't automatically record calculation history or create formal documentation trails. Engineering projects requiring ISO 9001 compliance or regulatory documentation need manual record-keeping of inputs, outputs, and conversion factors used. Professional engineering software provides built-in documentation features.
Limited Integration Capabilities
Standalone web calculators don't integrate with engineering software, spreadsheets, or databases. Each conversion requires manual input and output transfer. For workflows involving hundreds of conversions, programmatic solutions (APIs, Excel formulas, Python scripts) are more efficient than repeated web calculator use.
The Balanced Perspective
Pressure conversion calculators excel at what they're designed for: fast, accurate unit conversion for everyday engineering, scientific, and practical applications. They save enormous time and eliminate calculation errors for 95% of use cases. However, they're tools, not replacements for engineering knowledge. The most effective approach combines calculator efficiency with professional understanding of pressure principles, application-specific requirements, and safety considerations. Use calculators confidently for routine conversions, but engage qualified professionals for safety-critical systems, regulatory compliance, and complex applications where context matters as much as mathematical accuracy.
Universal Conversion Formula
PB = PA × (CFA→Pa / CFB→Pa)
Where:
- • PA = Pressure value in Unit A (input pressure)
- • PB = Pressure value in Unit B (converted pressure)
- • CFA→Pa = Conversion factor from Unit A to Pascals
- • CFB→Pa = Conversion factor from Unit B to Pascals
Two-Step Process Explanation:
Step 1: Convert to Pascals (Universal Base Unit)
PPascals = PA × CFA→Pa
Step 2: Convert from Pascals to Target Unit
PB = PPascals / CFB→Pa
Standard Conversion Factors to Pascals
| Unit | Symbol | Conversion Factor (to Pa) | Category |
|---|---|---|---|
| Pascal | Pa | 1 | SI (Base) |
| Kilopascal | kPa | 1,000 | SI |
| Megapascal | MPa | 1,000,000 | SI |
| Bar | bar | 100,000 | SI |
| Millibar | mbar | 100 | SI |
| Pound per Square Inch | PSI | 6,894.757 | Imperial |
| Atmosphere (Standard) | atm | 101,325 | Atmospheric |
| Torr | torr | 133.322 | Vacuum |
| Millimeters of Mercury | mmHg | 133.322 | Column (Hg) |
| Inches of Mercury | inHg | 3,386.389 | Column (Hg) |
| Inches of Water (4°C) | inH&sub2;O | 249.089 | Column (H&sub2;O) |
Detailed Conversion Examples
Example 1: Basic Conversion (Simple)
Task: Convert 5 bar to PSI
Step 1: Convert bar to Pascals
PPa = 5 bar × 100,000 Pa/bar = 500,000 Pa
Step 2: Convert Pascals to PSI
PPSI = 500,000 Pa ÷ 6,894.757 Pa/PSI = 72.52 PSI
✓ Result: 5 bar = 72.52 PSI
Verification: 5 × 14.5 ≈ 72.5 ✓ (quick approximation confirms result)
Example 2: Weather Pressure (Moderate)
Task: Convert 29.92 inHg (standard atmospheric pressure) to millibars
Step 1: Convert inches of mercury to Pascals
PPa = 29.92 inHg × 3,386.389 Pa/inHg = 101,325 Pa
(This is exactly 1 standard atmosphere by definition)
Step 2: Convert Pascals to millibars
Pmbar = 101,325 Pa ÷ 100 Pa/mbar = 1,013.25 mbar
(Note: 1 mbar = 1 hPa, so this is also 1,013.25 hPa)
✓ Result: 29.92 inHg = 1,013.25 mbar
This is standard sea-level atmospheric pressure used in meteorology
Example 3: Hydraulic System (Complex)
Task: Convert 3,500 PSIG (gauge) to MPa (absolute) at sea level
Step 1: Convert gauge pressure to absolute pressure
PPSIA = 3,500 PSIG + 14.7 PSIatm = 3,514.7 PSIA
(Must add atmospheric pressure for absolute pressure)
Step 2: Convert PSIA to Pascals
PPa = 3,514.7 PSI × 6,894.757 Pa/PSI = 24,229,805 Pa
Step 3: Convert Pascals to Megapascals
PMPa = 24,229,805 Pa ÷ 1,000,000 Pa/MPa = 24.23 MPa
✓ Result: 3,500 PSIG = 24.23 MPa (absolute)
Typical hydraulic excavator system pressure range
Excel/Google Sheets Implementation
Generic Conversion Formula:
Example: Convert cell A1 from bar to PSI:
Where 100,000 = bar-to-Pa factor, and 6,894.757 = PSI-to-Pa factor
How do I know if a pressure reading is gauge or absolute?
Check for suffixes: PSIG, barg (gauge) or PSIA, bara (absolute). If unlabeled, most industrial pressure gauges show gauge pressure (relative to atmospheric). Tire gauges, hydraulic gauges, and compressed air systems typically use gauge pressure. Absolute pressure is common in thermodynamic calculations, gas laws, and vacuum measurements. When in doubt, context helps: tire pressure at "0 PSI" means flat tire (atmospheric pressure), confirming it's gauge pressure.
Why do weather reports show different units in different countries?
Historical meteorological traditions and measurement systems vary globally. The United States uses inches of mercury (inHg) for barometric pressure, stemming from mercury barometer technology. Europe and most of the world use hectopascals (hPa) or millibars (mb), which are equivalent. Aviation internationally uses hPa for altimeter settings. Standard atmospheric pressure is 29.92 inHg, 1,013.25 hPa, or 1,013.25 mb — all representing the same physical pressure.
Can I use this calculator for vacuum pressure conversions?
Yes. Vacuum pressure below atmospheric can be expressed as negative gauge pressure or as low absolute pressure. For example, 25 inHg vacuum (gauge reading) equals 4.92 inHg absolute (29.92 - 25), which converts to approximately 16.7 kPa absolute. Enter the absolute pressure value into the calculator. Torr and millibar are commonly used for vacuum measurements in scientific equipment. Remember: perfect vacuum = 0 Pa absolute = -14.7 PSIG at sea level.
What's the difference between bar and atmosphere?
Bar is a convenient metric unit (100,000 Pa exactly), while atmosphere (atm) represents actual average sea-level atmospheric pressure (101,325 Pa). 1 bar = 0.9869 atm, so they're close but not identical. Bar is preferred in engineering for its round-number relationship to pascals. Atmosphere is used in chemistry and physics as a natural reference point. For practical purposes, 1 bar ≈ 1 atm ≈ 14.5 PSI, but use exact values for precision work.
How does altitude affect pressure readings?
Atmospheric pressure decreases approximately 1 inHg (or 3.4 kPa) per 1,000 feet elevation gain. At 5,000 feet, atmospheric pressure is about 24.9 inHg (84.3 kPa) instead of sea-level's 29.92 inHg (101.3 kPa). This affects gauge-to-absolute conversions: add actual local atmospheric pressure, not standard 14.7 PSI. High-altitude locations need altitude correction for accurate absolute pressure calculations. Gauge pressure readings remain unaffected since they measure relative to local atmospheric pressure.
Are torr and mmHg the same unit?
Almost identical but technically different. Torr is defined exactly as 1/760 of standard atmosphere (133.322 Pa), while mmHg depends on mercury density, local gravity, and temperature. At 0°C and standard gravity, 1 mmHg ≈ 1 torr with difference <0.000015%. For most practical purposes, they're interchangeable. Scientific vacuum work and metrology prefer torr for its exact definition. Medical blood pressure traditionally uses mmHg but increasingly adopts torr for consistency.
Why does my tire pressure change with temperature?
Gay-Lussac's Law: pressure increases with temperature for constant volume. Tire pressure typically increases 1-2 PSI per 10°F temperature rise. Cold morning tires at 32 PSI might read 35 PSI after highway driving in summer heat. This is normal physics, not a leak or over-inflation. Set tire pressure when "cold" (parked 3+ hours) to match manufacturer specifications. Unit conversion doesn't account for temperature effects — it only converts numerical values between measurement systems.
How precise should my pressure conversions be?
Match precision to measurement accuracy. Tire pressure gauges accurate to ±0.5 PSI don't need more than 1 decimal place in conversions. Scientific instruments with ±0.1% accuracy warrant 3-4 significant figures. Engineering specifications typically use 2-3 decimal places. Excessive precision (8+ decimals) is meaningless when source measurement has ±1-2% error. Use "significant figures" principle: final result precision should match least precise input measurement.
What's the difference between PSI and PSIA vs. PSIG?
PSI = generic pounds per square inch (context-dependent). PSIA = absolute pressure (includes atmospheric). PSIG = gauge pressure (relative to atmospheric). Relationship: PSIA = PSIG + atmospheric pressure (typically 14.7 PSI at sea level). Example: tire at 32 PSIG equals 46.7 PSIA. Thermodynamic formulas require PSIA. Industrial gauges show PSIG. Always clarify which system specifications use to avoid 14.7 PSI errors.
Can I convert water pressure from feet to PSI?
Yes, but that's technically a "head pressure" calculation, not unit conversion. Water pressure increases 0.433 PSI per foot of depth (or 1 PSI per 2.31 feet). For conversion between actual pressure units: 1 foot of water column (ftH&sub2;O) = 2,989 Pa = 0.433 PSI. This calculator handles ftH&sub2;O, inH&sub2;O, and other water column units. For well depth or water tower height calculations, multiply depth in feet by 0.433 to get PSI pressure.
Why are there different inH&sub2;O conversion factors?
Water density varies with temperature: 1 inH&sub2;O at 4°C (maximum density) = 249.089 Pa, while at 60°F = 248.843 Pa, and at 68°F = 248.64 Pa. Differences are small (<0.2%) but matter for precision HVAC and differential pressure measurements. Most calculators and industrial standards default to 4°C (39.2°F). If specifications cite a different temperature, use that specific conversion factor. For non-critical applications, the variation is negligible.
How do I convert pressure for gas cylinder specifications?
Gas cylinders specify service pressure (working pressure) and test pressure, usually in PSI (US) or bar (Europe). These are gauge pressures (PSIG/barg). Common cylinder ratings: 2,000 PSI (138 bar) for industrial gases, 3,000 PSI (207 bar) for breathing air, 200-300 bar for scuba tanks. Convert using this calculator's bar/PSI functions. Always verify if specification is gauge or absolute — cylinder ratings are virtually always gauge pressure.
Is this calculator accurate enough for engineering calculations?
Yes, for preliminary design, troubleshooting, and non-safety-critical calculations. Conversion factors are from NIST standards with full precision. However, final engineering designs requiring code compliance, safety factor calculations, or regulatory approval need professional engineer verification and documented calculation methods. Use this calculator confidently for concept development, equipment selection, and field diagnostics. For pressure vessel design, medical equipment, or life-safety systems, engage licensed professional engineers.
What pressure units do different industries prefer?
Automotive: PSI (US), bar (Europe). HVAC: PSI, inH&sub2;O for ductwork. Hydraulics: PSI, bar, MPa. Vacuum science: torr, mbar, Pa. Meteorology: inHg (US), hPa/mbar (global). Medical: mmHg (blood pressure), cmH&sub2;O (respiratory). Aerospace: PSI, kPa. Chemical engineering: bar, kPa, atm. Oil & gas: PSI, bar. Understanding industry norms helps select appropriate units for specifications and communication.
Why does my calculated pressure differ slightly from reference tables?
Minor discrepancies (<0.1%) arise from rounding differences in conversion factors. Some references use 1 PSI = 6.895 kPa (rounded), while precise value is 6.894757. Historical references may use slightly different standard definitions (e.g., older atmospheric pressure standards). Temperature-dependent units (water/mercury columns) vary with assumed temperature. For critical work, verify which standard your reference uses and match it. For everyday applications, differences are negligible.
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Authoritative Standards & References
NIST (National Institute of Standards and Technology)
Official US measurement standards and conversion factors. Definitive source for precise conversion constants.
ISO 80000-4:2019
International standard for mechanics quantities and units, including comprehensive pressure unit definitions.
ASME (American Society of Mechanical Engineers)
Pressure vessel codes, boiler standards, and engineering pressure specifications for mechanical systems.
BIPM (Bureau International des Poids et Mesures)
International measurement standards organization maintaining SI unit definitions including the pascal.
Further Learning
Engineering Fundamentals
- • Fluid mechanics textbooks covering pressure principles
- • Thermodynamics courses for gas pressure relationships
- • Engineering unit conversion reference manuals
Professional Development
- • HVAC technician certification programs
- • Hydraulic system design courses
- • Industrial instrumentation training
Before You Calculate: Preparation Checklist
1. Identify Your Source Unit
Confirm the exact unit of your pressure measurement:
- ✓ Check equipment labels and documentation
- ✓ Look for gauge (G) or absolute (A) suffixes
- ✓ Verify temperature standard for water/mercury columns
- ✓ Note any regional or industry-specific conventions
2. Determine Gauge vs. Absolute
Critical decision affecting accuracy:
- ✓ Most industrial gauges show gauge pressure
- ✓ Thermodynamic calculations need absolute
- ✓ Add atmospheric pressure if converting to absolute
- ✓ Subtract atmospheric if converting from absolute
3. Know Your Required Precision
Match output precision to application needs:
- ✓ Field measurements: 1-2 decimal places
- ✓ Engineering specifications: 2-3 decimals
- ✓ Scientific research: 3-5 significant figures
- ✓ Metrology/calibration: Full precision
4. Consider Environmental Factors
Account for conditions affecting pressure:
- ✓ Altitude: Affects atmospheric pressure baseline
- ✓ Temperature: Influences gas pressure (if applicable)
- ✓ Humidity: Can affect some low-pressure measurements
- ✓ Local gravity: Varies slightly by location
Using the Calculator Effectively
Enter Your Pressure Value
Type numerical value in the input field. Use decimal points for fractions (e.g., 2.5, not 2 1/2). Scientific notation acceptable for extreme values.
Select Your Source Unit
Click the unit you're converting FROM. Popular units appear as quick-select buttons. All 33+ units available via dropdown or tabs.
Review All Conversions Instantly
Results update in real-time. Browse by category (SI, Imperial, Atmospheric, Column) or view all simultaneously. Compare multiple units side-by-side.
Copy or Switch Units
Click copy button next to any result to save to clipboard. Click the result card itself to make it the new input unit for reverse conversion.
After Calculation: Verification & Next Steps
Verify Results Make Sense
Quick sanity checks:
- • Is the magnitude reasonable for the application?
- • Does 1 bar ≈ 14.5 PSI approximation hold?
- • Are atmospheric conversions near 101 kPa / 14.7 PSI?
- • Do results align with known reference points?
Document Your Conversion
For professional work, record:
- • Original value and unit
- • Converted value and target unit
- • Date and source of conversion
- • Any assumptions (gauge/absolute, temperature)
Apply Results Appropriately
Use converted pressures for:
- • Equipment specification comparisons
- • International project collaboration
- • Compliance with regional standards
- • Input to subsequent engineering calculations
When to Recalculate
Update conversions if:
- • Source measurement changes or is updated
- • Environmental conditions vary significantly
- • Different unit standards are required
- • Precision requirements increase
Troubleshooting Common Issues
❌ Result seems too high or too low
→ Check gauge vs. absolute pressure. Verify you selected correct source unit. Confirm decimal point placement.
❌ Calculator shows error or no results
→ Ensure numerical input only (no letters). Avoid special characters except decimal point and negative sign for vacuum.
❌ Results don't match reference table
→ Reference may use rounded conversion factors or different temperature standards. Verify both use same standard definitions.
❌ Need more or less precision
→ Copy full-precision result and round manually to match your measurement accuracy. Don't round during intermediate calculations.