BMI Calculator
Body Mass Index (BMI) is weight in kilograms divided by height in meters squared. For adults, the WHO classes a BMI under 18.5 as underweight, 18.5–24.9 as healthy, 25–29.9 as overweight and 30 or more as obesity. This calculator accepts metric or feet and inches and shows your healthy weight range.
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How to use the BMI Calculator
- Choose Metric (kg, cm) or US / Imperial (lb, ft, in).
- Enter your weight.
- Enter your height in centimeters, or in feet and inches.
- Read your BMI, category, healthy weight range and BMI Prime.
Features
- Metric (kg, cm) and US units (lb, feet and inches)
- WHO adult categories including obesity classes I–III
- Healthy weight range for your height
- BMI Prime and a visual scale
- Exact unit conversion (1 lb = 0.45359237 kg, 1 in = 2.54 cm)
- Range checks for unrealistic heights and weights
Frequently asked questions
How is BMI calculated?
BMI = weight (kg) ÷ height (m)². In US units, BMI = 703 × weight (lb) ÷ height (in)². For example, 70 kg at 1.75 m gives 22.9.
What is a healthy BMI?
For adults, a BMI from 18.5 to 24.9 is classed as healthy weight by the World Health Organization.
Is BMI accurate for everyone?
No. BMI does not measure body fat directly and can misclassify muscular people, older adults and some ethnic groups. It is not used for children, teenagers or pregnancy.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the upper limit of the healthy range. A value above 1.00 means your BMI is above the healthy range.
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Built and reviewed by Naqash Thaheem, Technical Project Manager. Last reviewed 2026-09-24.