BMI calculator
This calculator works out Body Mass Index from a height and a weight, then places the result into one of the four adult weight categories set out by the NHS. It also shows the weight range that keeps that height inside the NHS healthy BMI band. Figures are general information, not a diagnosis.
How is BMI calculated?
BMI is calculated by dividing weight in kilograms by the square of height in metres.
The tool places that figure in one of four adult categories used by the NHS.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25 to 29.9 | Overweight |
| 30 or over | Obese |
Feet, inches, stones and pounds are converted to metric before the calculation runs, so an imperial entry gives the same BMI as its metric equivalent.
BMI is a screen rather than a verdict, because it cannot tell muscle from fat.
A very muscular person can sit in the overweight band while carrying little fat, and someone with a healthy BMI can still carry excess fat around the waist.
The NHS notes that the healthy range starts lower for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, because health risks can appear at a lower BMI for these groups.
What would a BMI look like for an example height and weight?
Take a height of 1.75 m and a weight of 78 kg.
Squaring the height gives 3.06, and 78 divided by 3.06 is about 25.5, which falls inside the NHS overweight range of 25 to 29.9.
For that height, the NHS healthy weight range of 18.5 to 24.9 corresponds to a weight of roughly 57 kg to 76 kg.
This is general information rather than a recommendation to change weight, and a GP can advise on personal circumstances.
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 BMI reading is a starting point rather than a plan. This calculator gives general information only, and does not recommend losing or gaining weight. Anyone wanting advice about their weight or health should speak to a GP, who can assess personal circumstances and, where appropriate, point to NHS Better Health resources.
What would a BMI look like for an example height and weight?
For a height of 1.75 m and a weight of 78 kg, BMI works out at about 25.5, calculated as weight in kilograms divided by height in metres squared. A BMI of 25.5 falls inside the NHS overweight range of 25 to 29.9. For that same height, the NHS healthy weight range of 18.5 to 24.9 corresponds to a weight of roughly 57 kg to 76 kg.
Sources & Rate Verification
Rates verified against official statutory guidance on 6 September 2026.