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BMI Calculator

Calculate your Body Mass Index from height and weight, in metric or imperial units. See your BMI value and which category it falls into.

The BMI Calculator is a free online tool. Enter your height and weight in metric (cm/kg) or imperial (ft-in/lb) and it instantly shows your Body Mass Index and the standard WHO category. BMI is a general guide and does not account for muscle mass or body composition.
BMI Calculator

How to use

1

How BMI is calculated

BMI = weight (kg) ÷ height (m)². For imperial, BMI = 703 × weight (lb) ÷ height (in)². The same formula is used worldwide for adults aged 20 and over.

2

The standard categories

Under 18.5 is underweight, 18.5–24.9 is healthy, 25–29.9 is overweight, and 30 or above is obese — ranges set by the World Health Organization.

3

What BMI does not tell you

BMI is a rough screening tool. It cannot tell muscle from fat, so very muscular people can read as overweight. It is also less reliable for children, older adults and pregnant women.

💡 Did you know?

BMI was devised in the 1830s by Belgian mathematician Adolphe Quetelet — it was originally called the Quetelet Index and was never intended to measure individual health, only to describe populations.

Reviewed for 2026. Built by a UK-based qualified primary teacher and FA Level 2 coach as part of 247QuickTools' free utility-tools project.