1. Pick units
Pick metric (cm/kg) or imperial (ft/in/lb) units — whichever you already have on hand.
Back to tools
BMI calculator
Calculate Body Mass Index.
Unit
BMI
22.9
Normal
Underweight
< 18.5
Normal
18.5–24.9
Overweight
25–29.9
Obese
30+
BMI is calculated in this browser tab. Nothing is uploaded.
How it works
2. Type height + weight
Type your height and weight. The BMI updates live; the category lands in one of four WHO bands.
3. Compare
Compare against the reference ranges shown alongside the result. The numbers never leave the page.
About the BMI Calculator tool
The BMI Calculator works out your Body Mass Index from your height and weight in either metric (cm and kg) or imperial (feet, inches, and pounds) units. The figure updates live as you type and lands in one of the four World Health Organization adult bands — underweight, normal, overweight, or obese — shown alongside the reference ranges so you can see where you sit. The formula is weight in kilograms divided by height in metres squared, with the equivalent 703 × lb ÷ in² used for imperial inputs.
BMI is a quick, widely used screening number, useful as a rough check or a starting point for a conversation with a clinician. It is worth knowing its limits: it does not distinguish muscle from fat and is not appropriate for very athletic builds, children, or pregnancy, so it should be paired with clinical judgement rather than treated as a diagnosis. Your height and weight stay in your browser tab and are never uploaded, and the tool is free, needs no account, and works offline once loaded.
Frequently asked questions
What's the formula?
BMI = weight (kg) divided by height (m) squared. The imperial form is 703 × weight (lb) ÷ height (in)². Both reduce to the same value.
Which BMI categories?
We use the WHO adult bands: under 18.5 = underweight, 18.5–24.9 = normal, 25–29.9 = overweight, 30+ = obese.
When is BMI not a good measure?
BMI is a population-level screening tool, not a diagnosis. It doesn't distinguish muscle from fat and isn't appropriate for very athletic builds, children, or pregnancy. Always pair with clinical judgement.
Is anything sent to a server?
No. Your height and weight stay in the browser tab. Nothing is uploaded.