BMI Calculator

Calculate your Body Mass Index from height and weight — metric or US units — and see your WHO category instantly.

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WHO ranges: Underweight < 18.5 · Normal 18.5–24.9 · Overweight 25–29.9 · Obese ≥ 30
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About this tool

Body Mass Index (BMI) is the standard screening measure for weight relative to height, used by the WHO and doctors worldwide. This calculator works in metric (cm, kg) or US units (feet/inches, pounds) and shows your BMI with its category the moment you finish typing.

The formula is weight in kilograms divided by height in metres squared. The WHO adult ranges are: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30 or above obese.

BMI is a useful population-level screening tool but not a diagnosis: it cannot distinguish muscle from fat, so athletes often score "overweight" while being very fit, and healthy ranges can differ slightly by ethnicity and age. Treat your result as a starting point for a conversation with a health professional, not medical advice.

How to use

  1. Choose metric (cm, kg) or US (ft/in, lbs) units.
  2. Enter your height and weight.
  3. Read your BMI and WHO category — it updates as you type.

Frequently asked questions

For adults the WHO defines 18.5–24.9 as the normal range. Below 18.5 is underweight; 25–29.9 is overweight; 30+ is obese.

BMI = weight (kg) ÷ height (m)². In US units: BMI = 703 × weight (lb) ÷ height (in)². This tool converts automatically.

Not very — muscle weighs more than fat, so muscular people often read "overweight" despite low body fat. Pair BMI with waist measurement or body-fat percentage.

The formula is the same, but interpretation differs: children and teens use age/sex percentile charts, and some guidance adjusts ranges for older adults and certain ethnicities.

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