About BMI Calculator
Body mass index divides your weight by the square of your height. That is the entire calculation, and its simplicity is both why it is used everywhere and why it misleads so often.
What BMI genuinely does well is describe populations. Across thousands of people it tracks health outcomes usefully, which is why public health bodies rely on it. What it cannot do is tell you what your weight is made of — muscle weighs more than fat for the same volume, so a rugby player and someone carrying excess fat can share a BMI of 28 and be in completely different health.
The thresholds have limits of their own. The healthy band of 18.5 to 24.9 was derived largely from European populations, and several health bodies including the NHS use lower cut-offs for people of South Asian, Chinese and Middle Eastern descent, where health risks appear at a lower BMI.
How to use it
Choose metric or imperial
Switching converts what you have already entered rather than reinterpreting it.
Enter your details
Everything is calculated in your browser as you type. Nothing is sent anywhere.
Read the result in context
Each figure is shown with what the formula can and cannot tell you.