BMI and waist-to-height calculator
Body mass index (BMI) compares your weight with your height. Waist-to-height ratio shows how much weight you carry around your middle. Together they give a rough picture of weight-related health risk.
What your BMI means
For most adults, the World Health Organization bands are:
| BMI | Band |
|---|---|
| Under 18.5 | Below the healthy range |
| 18.5 to 24.9 | Healthy range |
| 25 to 29.9 | Overweight |
| 30 to 39.9 | Obesity |
| 40 or more | Severe obesity |
UK guidance from NICE recommends lower thresholds for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background, because health risks such as type 2 diabetes start to rise at a lower BMI. For these groups, overweight starts at 23 and obesity at 27.5. That's why our weight programme starts at a BMI of 25, or 23 with a weight-related condition.
What your waist tells you
Fat stored around the middle is linked more closely to heart disease and type 2 diabetes than weight alone. A simple rule from NICE: keep your waist to less than half your height.
- 0.4 to 0.49: healthy range
- 0.5 to 0.59: increased health risk
- 0.6 or more: high health risk
To measure your waist, find the point halfway between your lowest rib and the top of your hip bone. Breathe out normally and measure around your body there, with the tape level and snug but not tight.
What these numbers can't tell you
- Muscle. Muscle is heavier than fat, so very muscular people can have a high BMI and be healthy.
- Age. Older adults tend to lose muscle, so a "healthy" BMI can hide low muscle mass.
- Your whole health. Blood pressure, blood sugar, cholesterol, sleep and fitness matter as much as any single number.
That's why a doctor looks at the whole picture before recommending anything. If your BMI is below 18.5, or you've lost weight without trying, please see your GP.