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BMI Calculator

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What is the BMI Calculator?

The BMI Calculator works out your body mass index from height and weight, in metric (cm and kg) or imperial (feet, inches and pounds), and shows where the result falls on the World Health Organization scale: underweight, healthy, overweight or obese. It also shows the weight range that would count as healthy for your height, so the number comes with context instead of a bare label. It runs in your browser and nothing is stored.

How to use it

Choose metric or imperial.
Enter height and weight.
Read your BMI, the category, and the healthy weight range for your height.

The formula and the categories

BMI is weight in kilograms divided by height in metres squared. In imperial units it is weight in pounds divided by height in inches squared, multiplied by 703. The WHO categories for adults are under 18.5 underweight, 18.5 to 24.9 healthy, 25 to 29.9 overweight, and 30 and above obese, with obesity split into classes I, II and III at 35 and 40. Some countries use lower thresholds for populations with different body composition; the guide explains which. Read BMI explained: formula, categories and limits for the detail.

What BMI does not tell you

BMI is a population screening tool, not a diagnosis. It cannot distinguish muscle from fat, so a muscular athlete can read as overweight, and it says nothing about where fat is carried, which matters more for health risk. It is also not designed for children (who use age-and-sex percentile charts), pregnant women, or people over 65. Use it as one signal alongside waist measurement, fitness and a conversation with a doctor.

Related tools

Work out daily energy needs with the Calorie Calculator, convert your measurements with the Unit Converter, or calculate your exact age for age-adjusted charts with the Age Calculator.

Read the guide

How BMI Is Calculated, What the Categories Mean, and When to Ignore It

The BMI formula in metric and imperial, WHO categories and the lower Asian thresholds, the six situations where BMI misleads, and the two simple measurements worth pairing it with.