BMI Calculator
Body Mass Index in metric, imperial or UK units (stones and pounds), with the WHO adult weight category ranges.
Last updated
How to calculate your BMI
- Choose metric (cm and kg), imperial (feet, inches and pounds) or UK (feet, inches, stones and pounds).
- Enter your height and weight.
- Read your BMI and which adult weight category it falls in.
The formula
BMI = weight (kg) ÷ height (m)². The World Health Organisation's adult categories are: under 18.5 = underweight, 18.5–24.9 = normal weight, 25–29.9 = overweight, 30 and above = obese. These ranges were developed from population-level data and are a rough screening tool, not a diagnosis — talk to a healthcare provider for an assessment that accounts for your individual body composition.
Nothing entered here is sent to a server — the entire calculation runs as JavaScript in your browser tab.
Questions about BMI
How is BMI calculated?
Weight in kilograms divided by height in metres squared. Someone 1.75 m tall weighing 70 kg has a BMI of 70 ÷ 1.75² ≈ 22.9.
What is a healthy BMI?
For adults, the World Health Organisation’s healthy range is 18.5 to 24.9. Under 18.5 is underweight, 25 to 29.9 overweight and 30 or more obese.
Can I enter my weight in stones and pounds?
Yes. Choose UK units and enter your height in feet and inches and your weight in stones and pounds.
Is BMI accurate for everyone?
No. It doesn’t tell muscle from fat, so very muscular people can score as overweight, and healthy ranges differ for some ethnic groups and for children. It’s a screening guide, not a diagnosis; a doctor can assess you properly.