How to use the BMI Calculator
- Choose your units: Metric (cm and kg), US (feet, inches and pounds) or UK (feet, inches and stones).
- Enter your height and weight. Age and sex are optional for adults — if you enter an age under 20, the calculator switches to BMI-for-age percentiles.
- Tick the background box if you are of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background. NICE recommends lower cut-offs for these groups.
- Press Calculate BMI to see your BMI, category, healthy weight range, BMI Prime and ponderal index.
The BMI formula
Body mass index is your weight divided by the square of your height: BMI = weight (kg) ÷ height (m)². In US units the formula is BMI = 703 × weight (lb) ÷ height (in)². For example, a person who is 1.75 m tall and weighs 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which is in the healthy weight range.
BMI categories for adults
For adults aged 20 and over, the same categories are used for women and men of every age. They come from the World Health Organization:
| BMI (kg/m²) | Adult category (WHO) |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| 40 or more | Obesity class III |
Some people have a higher health risk at a lower BMI. For adults of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, NICE guidance treats a BMI of 23 or more as overweight and 27.5 or more as obesity. In India and much of Asia, the Asia-Pacific BMI ranges are used.
Healthy weight range for your height
Your healthy weight range is the weight that gives a BMI from 18.5 to 24.9 at your height. The calculator shows it in your own units, together with roughly how much you would need to gain or lose to reach the nearest edge of the range. The table below shows the range for common heights.
| Height | BMI 18.5 | BMI 24.9 | BMI 30 |
|---|---|---|---|
| 150 cm | 41.6 kg | 56.0 kg | 67.5 kg |
| 155 cm | 44.4 kg | 59.8 kg | 72.1 kg |
| 160 cm | 47.4 kg | 63.7 kg | 76.8 kg |
| 165 cm | 50.4 kg | 67.8 kg | 81.7 kg |
| 170 cm | 53.5 kg | 72.0 kg | 86.7 kg |
| 175 cm | 56.7 kg | 76.3 kg | 91.9 kg |
| 180 cm | 59.9 kg | 80.7 kg | 97.2 kg |
| 185 cm | 63.3 kg | 85.2 kg | 102.7 kg |
| 190 cm | 66.8 kg | 89.9 kg | 108.3 kg |
| 195 cm | 70.3 kg | 94.7 kg | 114.1 kg |
What BMI can and cannot tell you
BMI is a quick screening tool used by doctors, insurers and public-health researchers because it only needs height and weight. It does not measure body fat directly. Muscular people can have a high BMI without excess fat, and older adults can have a normal BMI while carrying more fat and less muscle. Waist size adds useful information: NICE suggests keeping your waist to less than half your height (a waist-to-height ratio under 0.5).
Looking for something more specific? Try the BMI Calculator for Women, the BMI Calculator for Men, the Child BMI Calculator for ages 2–19 or the BMI Calculator by Age. Read our guide to BMI for the background to every number.