Can children use this calculator?

This calculator is for adults 20+, children need age and sex-specific BMI percentiles from CDC growth charts

Combination of factors including genetics, diet, physical activity, sleep, stress, medications, and health conditions

BMI Calculator

Use our free BMI calculator to quickly check if you're underweight, normal weight, overweight, or obese. This BMI calculator uses your height and weight to estimate body fat and shows results instantly. Trusted by millions for accurate BMI calculations and health assessments.

Enter Your Details

Unit System

Age (optional)

years

Gender (optional)

Height *

Weight *

lbs

Formula: BMI = weight (kg) / height² (m²)

For US units: BMI = 703 × weight (lbs) / height² (in²)

Your Results

Enter your details

Fill in your height and weight to calculate your BMI and see personalized results.

What is Body Mass Index (BMI)?

Body Mass Index (BMI) tells you if your weight is healthy for your height. It's a simple number doctors use worldwide. You just need two things: your height and weight.

Think of BMI as a quick health check. A higher number usually means more body fat. A lower number might mean you're underweight. The sweet spot is between 18.5 and 24.9.

Doctors use BMI to spot potential health risks early. It helps them decide if you need more tests. It's not perfect, but it's been used for decades because it works for most people.

How Does BMI Work?

BMI compares your weight to your height using a math formula. Taller people naturally weigh more. The formula adjusts for this. That's why someone who's 6 feet tall can weigh more than someone who's 5 feet tall and still be healthy.

The calculation takes seconds. Enter your measurements, and you get your BMI instantly. Then you can see which weight category you fall into. No complicated steps or medical knowledge needed.

Who Should Use a BMI Calculator?

Adults aged 20 and older can use this calculator. Both men and women use the same formula. It works whether you're 25 or 75 years old.

Children and teens need different calculations. Their bodies are still growing. Kids use BMI percentiles that compare them to others their age and sex. If you're checking a child's BMI, use CDC growth charts instead.

Pregnant women shouldn't rely on BMI alone. Their weight naturally increases during pregnancy. Athletes with lots of muscle might also get misleading results. We'll explain those limitations later.

Why BMI Matters for Your Health

Your weight affects almost every part of your body. Extra weight puts stress on your heart. It makes your body work harder to pump blood. This can lead to high blood pressure and heart disease.

Being too thin has risks too. You might not get enough nutrients. Your bones could become weak. Your immune system might struggle to fight off sickness.

BMI helps you catch problems before they get serious. Knowing your number is the first step. Then you can talk to your doctor about what it means for you. Small changes can make a big difference over time.

Millions of people check their BMI every year. It's part of routine health checkups. Insurance companies use it. Researchers study it. You should know yours too.

BMI Formula

Calculate your Body Mass Index using these standard formulas

Metric Formula

BMI = \frac{weight\,(kg)}{height^2\,(m^2)}

Example: A person weighing 70 kg who is 1.75 m tall:

BMI = \frac{70}{1.75^2} = \frac{70}{3.06} = 22.9

US Standard Formula

BMI = 703 \times \frac{weight\,(lbs)}{height^2\,(in^2)}

Example: A person weighing 160 lbs who is 5'10" (70 inches):

BMI = 703 \times \frac{160}{70^2} = 703 \times \frac{160}{4900} = 23.0

BMI Categories (WHO Standards)

World Health Organization classification for adults age 20 and older

Category	BMI Range
Severe Thinness	< 16
Moderate Thinness	16 - 17
Mild Thinness	17 - 18.5
Normal	18.5 - 25
Overweight	25 - 30
Obese Class I	30 - 35
Obese Class II	35 - 40
Obese Class III	> 40

BMI Prime

A ratio showing how far your BMI is from the healthy weight threshold

Formula

BMI\,Prime = \frac{BMI}{25}

Where 25 is the upper limit of normal BMI range

Interpretation

Below 0.74
Underweight
0.74 to 1.0
Normal weight
1.0 to 1.2
Overweight
Above 1.2
Obese

Ponderal Index

A weight-height ratio more accurate for very tall or very short individuals

Formula

PI = \frac{weight\,(kg)}{height^3\,(m^3)}

Normal range: $11-15\,kg/m^3$

Why Use Ponderal Index?

The Ponderal Index cubes the height instead of squaring it like BMI. This provides a more accurate assessment for people at the extremes of height.

Better for tall people

BMI tends to overestimate body fat in very tall individuals

Better for short people

BMI tends to underestimate body fat in very short individuals

BMI Table for Adults

World Health Organization (WHO) BMI classification for adults 20 years and older

BMI Range (kg/m²)	Category	Health Risk
$< 16.0$	Severe Thinness	Malnutrition, weakened immunity
16.0 - 16.9	Moderate Thinness	Nutritional deficiency
17.0 - 18.4	Mild Thinness	Possible nutritional issues
18.5 - 24.9	Normal Weight	Lowest health risk
25.0 - 29.9	Overweight	Increased risk
30.0 - 34.9	Obese Class I	Moderate risk
35.0 - 39.9	Obese Class II	High risk
$\geq 40.0$	Obese Class III	Very high risk

BMI Chart for Adults

Visual guide showing BMI ranges by height and weight

$< 18.5$

Underweight

18.5-24.9

Normal

25.0-29.9

Overweight

$\geq 30$

Obese

Height	Weight (lbs)
	Normal	Overweight	Obese
5'0"	97-127	128-152	153+
5'3"	107-140	141-168	169+
5'6"	118-154	155-185	186+
5'9"	125-168	169-202	203+
6'0"	140-183	184-220	221+
6'3"	152-199	200-239	240+

BMI Table for Children and Teens

BMI percentile categories for ages 2-19 years (CDC growth charts)

Important Note About Children's BMI

BMI for children and teens uses percentiles that compare a child's measurements with others of the same age and sex. Children's body composition changes as they grow, so adult BMI categories don't apply. Always consult a pediatrician for proper assessment.

BMI Percentile Range	Weight Status Category
$< 5^{th}$ percentile	Underweight
$5^{th}$ to $< 85^{th}$ percentile	Healthy Weight
$85^{th}$ to $< 95^{th}$ percentile	Overweight
$\geq 95^{th}$ percentile	Obese

BMI Chart for Children and Teens

How BMI changes with age for boys and girls

Boys (2-20 years)

Age 5:BMI 14-17 (Normal)

Age 10:BMI 14-20 (Normal)

Age 15:BMI 17-23 (Normal)

Age 18:BMI 18-24 (Normal)

Girls (2-20 years)

Age 5:BMI 14-17 (Normal)

Age 10:BMI 14-20 (Normal)

Age 15:BMI 17-23 (Normal)

Age 18:BMI 18-24 (Normal)

Use CDC Growth Charts for Accurate Assessment

These are approximate ranges. For precise percentile calculations, use the official CDC BMI-for-age growth charts that account for exact age in months and sex. Our calculator is designed for adults only.

Visit CDC Growth Charts

Health Risks Associated with High BMI

According to the CDC and NIH, excess body weight increases your risk for these conditions

Type 2 Diabetes

Excess weight affects insulin resistance

Heart Disease

Coronary artery disease and heart attacks

High Blood Pressure

Hypertension damages blood vessels

Stroke

Blocked blood flow to the brain

Sleep Apnea

Breathing interruptions during sleep

Certain Cancers

Breast, colon, kidney, liver, gallbladder

High Cholesterol

Elevated LDL and triglycerides

Osteoarthritis

Joint pain from excess pressure

Gallbladder Disease

Gallstones and inflammation

Fatty Liver Disease

Fat buildup in liver cells

Mental Health Issues

Depression and anxiety

Kidney Disease

Chronic kidney problems

Health Risks Associated with Low BMI

Being underweight can also cause serious health problems

Malnutrition

Vitamin and mineral deficiencies

Weakened Immunity

Higher risk of infections

Osteoporosis

Weak, brittle bones

Anemia

Low red blood cell count

Fertility Issues

Hormonal imbalances affecting reproduction

Growth Problems

Especially in children and teens

Surgical Complications

Higher risk during operations

Hair Loss

Thinning hair from poor nutrition

Fatigue

Low energy and weakness

Limitations of BMI

BMI is a useful screening tool, but it has important limitations to consider

BMI Does Not Measure:

•Body fat percentage directly
•Muscle mass vs fat mass
•Fat distribution (belly fat vs other areas)
•Bone density or frame size
•Metabolic health markers

BMI May Be Inaccurate For:

•Athletes and bodybuilders (muscle weighs more)
•Older adults who have lost muscle
•Pregnant or breastfeeding women
•People of Asian descent (may underestimate risk)
•Very tall or very short individuals

Consider Measuring Waist Circumference Too

The Mayo Clinic recommends checking waist size along with BMI. Excess belly fat increases health risks even if BMI is normal.

For Men

Waist over 40 inches (102 cm) = higher risk

For Women

Waist over 35 inches (88 cm) = higher risk

How to Maintain a Healthy Weight

Evidence-based strategies recommended by health organizations

Eat a Balanced Diet

Focus on fruits, vegetables, whole grains, lean proteins, and healthy fats. Limit processed foods, sugary drinks, and excessive sodium.

Stay Physically Active

Aim for at least 150 minutes of moderate activity per week. Include strength training exercises twice weekly.

Monitor Portion Sizes

Use smaller plates, read food labels, and be mindful of serving sizes. Eating slowly helps you recognize fullness cues.

Get Quality Sleep

Poor sleep disrupts hunger hormones. Aim for 7-9 hours nightly. Maintain a consistent sleep schedule.

Manage Stress

Chronic stress can lead to emotional eating. Try meditation, deep breathing, or regular physical activity.

Consult Healthcare Providers

Talk to your doctor about your BMI and overall health. They can help create a personalized plan for your goals.

Frequently Asked Questions

Common questions about BMI and body weight

What is a healthy BMI range?

For adults, a BMI between 18.5 and 24.9 is considered healthy. This range is associated with the lowest risk of weight-related health problems.

Is BMI accurate for athletes?

BMI may overestimate body fat in athletes because muscle weighs more than fat. A muscular person might have a high BMI but low body fat percentage.

Does BMI differ by age?

For adults 20+, the same BMI categories apply regardless of age. However, older adults tend to have more body fat at the same BMI than younger adults.

Is BMI the same for men and women?

Yes, the same BMI formula and categories apply to both sexes. However, women typically have more body fat than men at the same BMI.

How often should I check my BMI?

Check your BMI periodically during routine health checkups. If you're actively trying to gain or lose weight, monthly checks can help track progress.

Can children use this BMI calculator?

This calculator is for adults 20+. Children and teens (ages 2-19) need age and sex-specific BMI percentiles calculated with growth charts.

What causes obesity?

Obesity results from a combination of factors including genetics, diet, physical activity levels, sleep patterns, stress, medications, and underlying health conditions.

When should I see a doctor about my weight?

Consult a healthcare provider if your BMI is outside the healthy range, if you've had significant unintentional weight changes, or if you have concerns about your weight.

Does BMI predict disease risk?

BMI is a screening tool, not a diagnostic one. A high BMI indicates increased risk but doesn't guarantee health problems. Other factors like family history and lifestyle matter too.

What's the difference between BMI and body fat percentage?

BMI estimates body fat using height and weight. Body fat percentage measures actual fat tissue.

Related Health Calculators

Complete your health assessment with these tools

BMR Calculator

Calories Burned Calculator

Calorie Calculator

Ideal Weight Calculator