Math Calculators

BMI Calculator

Calculate your Body Mass Index in metric (kg/cm) or imperial (lb/ft/in). Shows your BMI value, weight category, and healthy weight range instantly.

Metric & Imperial
BMI Category
Healthy Weight Range
Instant Results
Browser-only

Weight (kg)

Enter body weight

Height (cm)

Enter height without shoes

Enter height and weight to calculate BMI

BMI calculator

Body Mass Index (BMI) compares adult weight with height. Enter metric measurements in kilograms and centimetres, or imperial measurements in pounds, feet, and inches. The calculation runs in your browser and shows a BMI value, adult WHO category, and estimated weight range for the entered height.

Adult BMI categories

Category	BMI
Underweight	Below 18.5
Normal weight	18.5–24.9
Overweight	25.0–29.9
Obesity, Class I	30.0–34.9
Obesity, Class II	35.0–39.9
Obesity, Class III	40.0 or higher

These ranges are screening categories for adults. They are not a diagnosis or a complete measure of health.

BMI formulas

Metric BMI divides weight in kilograms by height in metres squared:

const heightMetres = heightCentimetres / 100;
const bmi = weightKg / (heightMetres ** 2);

Imperial BMI uses pounds and total height in inches:

total_inches = feet * 12 + inches
bmi = 703 * weight_pounds / (total_inches ** 2)

Both formulas represent the same ratio after unit conversion. Use a measured height without shoes and a consistent weight unit.

Healthy weight range

For adults, the calculator converts the BMI range 18.5–24.9 into a weight range for the entered height. This estimate is useful for orientation, but it does not account for muscle mass, bone density, body-fat distribution, age, sex, or medical conditions.

Common uses and limitations

BMI can help compare weight trends over time, prepare questions for a healthcare appointment, or provide a quick population-level screening estimate. It is less informative for highly muscular athletes, older adults with low muscle mass, children and teens, and people who are pregnant.

Children and teens require age- and sex-specific percentile charts rather than adult cutoffs. Speak with a qualified healthcare professional before making decisions based only on BMI, especially when a result is unexpected or changing quickly.

Frequently Asked Questions

What is BMI?: Body Mass Index (BMI) is a numerical value calculated from height and weight. It is a widely used screening tool to categorize weight relative to height. BMI = weight(kg) / height(m)². For imperial units: BMI = (weight(lbs) / height(in)²) × 703.
What do the BMI categories mean?: WHO classifications: Below 18.5 = Underweight; 18.5–24.9 = Normal weight; 25.0–29.9 = Overweight; 30.0–34.9 = Obesity (Class I); 35.0–39.9 = Obesity (Class II); 40+ = Obesity (Class III).
Is BMI an accurate health indicator?: BMI is consistent and easy to calculate, but it is a population-level screening tool rather than a direct measurement of body fat or a definitive individual health assessment. It does not account for muscle mass, bone density, age, sex, or fat distribution. Athletes may have high BMI due to muscle, while older adults may have normal BMI with unhealthy fat levels. Consider BMI alongside waist measurement, activity, diet, medical history, and professional assessment.
What is the healthy BMI range?: The World Health Organization defines 18.5 to 24.9 as the healthy (normal) BMI range for adults. This range is associated with the lowest risk of weight-related health complications in large population studies.
Does BMI apply to children?: For children and teens (ages 2–19), BMI is interpreted differently using age- and sex-specific percentile charts (CDC growth charts). This tool is designed for adults only.
How is the healthy weight range calculated?: For adults, the healthy BMI range is 18.5–24.9. The calculator converts that range into an estimated healthy weight range for your entered height.
Is my BMI data private?: The calculator runs in your browser. Entered height and weight are not uploaded or stored by this tool.

Disclaimer

This tool is provided for general informational and utility purposes only. Results may be inaccurate, incomplete, outdated, or contain errors. Always verify results before relying on or using them.

Some tools may use AI, automated processing, third-party services, or server-side processing. Do not rely on these tools as a substitute for professional advice.

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