BMI Calculator: what your BMI means
A short guide to Body Mass Index — how it's calculated, what the categories mean, and what BMI can and can't tell you.
Open the BMI Calculator →What this tool does
The BMI Calculator works out your Body Mass Index from your height and weight, in metric or imperial units, then shows your category and the healthy weight range for your height. It runs entirely in your browser.
How BMI is calculated
BMI is your weight in kilograms divided by the square of your height in metres:
BMI = kg ÷ m². If you use imperial units, the calculator converts feet, inches
and pounds for you.
The categories
- Under 18.5 — underweight.
- 18.5–24.9 — healthy weight.
- 25–29.9 — overweight.
- 30 and above — obese.
The tool also shows the weight range that would put you in the healthy band for your height.
The limits of BMI
BMI is a quick population-level screen, not a diagnosis. It doesn't tell muscle from fat or account for age, sex, and body shape — so athletes can read as "overweight" despite low body fat. Treat it as a rough guide and speak to a healthcare professional for personal advice.
Your data stays private
Your height and weight are used only in your browser — nothing is uploaded.
FAQ
How is BMI calculated?
Weight (kg) divided by height (m) squared; imperial is converted automatically.
What is a healthy BMI?
For adults, roughly 18.5–24.9.
Is BMI accurate?
It's a screening tool, not a diagnosis — it ignores muscle, age and body composition.
This tool is for general information and is not medical advice.
Ready to try it? Open the BMI Calculator →