BMI calculator
Enter your height and weight to see your Body Mass Index, which NHS category it falls in, and the weight range that would put you in the healthy band.
How it works
BMI is your weight in kilograms divided by the square of your height in metres. The tool does that sum and places the result in one of the four NHS adult categories: under 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight, and 30 or over is in the obese range. If you enter imperial units, feet, inches, stones and pounds are converted to metric before the calculation, so the result is identical either way.
The number is a screen, not a verdict. BMI cannot tell muscle from fat, so a very muscular person can sit in the overweight band while carrying little fat, and someone with a healthy BMI can still carry too much fat around the waist. The NHS also notes that for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background the healthy range starts lower, because health risks can appear at a lower BMI. Treat a high reading as a prompt to look closer, not a diagnosis.
Worked example
Take someone 1.75 m tall who weighs 78 kg. Squaring the height gives 3.06, and 78 divided by 3.06 is about 25.5, which sits just inside the overweight band. For that height, a weight of roughly 57 kg to 76 kg would fall in the healthy range, so a few kilograms would move the reading back under 25. That is the kind of small, realistic target the NHS Better Health tools are built around.
Common questions
What is a healthy BMI?
For most adults a BMI from 18.5 to 24.9 is in the healthy weight range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or over is in the obese range. These are general NHS categories for adults, not a diagnosis.
How is BMI calculated?
BMI is your weight in kilograms divided by your height in metres squared. For example, 78 kg and 1.75 m gives 78 divided by 3.06, which is a BMI of about 25.5. The imperial option converts stones, pounds, feet and inches to metric first.
Is BMI accurate?
BMI is a quick screen, not a full picture. It does not separate muscle from fat, so very muscular people can read as overweight while carrying little fat. It also does not account for where fat sits. Waist measurement and a GP assessment give more detail.
Does BMI work the same for everyone?
No. The NHS notes that the healthy range sits lower for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, because the health risk can start at a lower BMI. Children and pregnant women are assessed differently.
What should I do if my BMI is high?
A single reading is only a starting point. If your BMI is in the overweight or obese range, small and steady changes to diet and activity help, and the free NHS Better Health tools or a GP can support a plan that fits you.