BMI Calculator
Body Mass Index (BMI) is a simple measure of whether your weight is in a healthy range for your height. It is a screening tool, not a diagnosis — muscle mass, age and body shape all matter.
Choose metric or imperial units, enter your weight and height, and see your BMI instantly.
How the calculation works
We believe numbers should be transparent. Here is the formula behind this calculator.
Worked example
Worked example: 70 kg, 175 cm
Important assumptions
- BMI is a screening measure for adults and does not account for muscle mass, age or ethnicity.
- The healthy weight range corresponds to a BMI of 18.5–24.9.
- Not suitable for children, pregnant women or athletes — see a health professional for guidance.
Frequently asked questions
Is BMI accurate?
It is a useful screening tool but not a complete picture. Very muscular people can have a high BMI with low body fat, and healthy ranges differ slightly by ethnicity. Use it as a starting point, not a verdict.
What is the difference between metric and imperial BMI?
The result is the same number either way — imperial just uses the 703 conversion factor. Pick whichever units you know: kg and cm, or pounds and inches.
What should I do if my BMI is outside the healthy range?
Speak to your GP or a qualified health professional before starting anything. Small, sustainable changes to diet and activity generally matter more than any single number.
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Related guides
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Browse financial guidesThese calculations are estimates for guidance only and are not professional financial, tax or legal advice. UK rates and rules change, so always verify important figures with official GOV.UK / HMRC information or speak to a qualified professional. See our full disclaimer.