Enter your height and weight, in metric or imperial, to see your body mass index, which category it falls in and the weight range that is healthy for your height.
Results are estimates for planning. Check the figures before you make a financial or health decision.
How the BMI works
Body mass index is your weight divided by your height squared: BMI = kg ÷ m². In imperial units the tool uses 703 × pounds ÷ inches².
It then places the result in the NHS adult ranges:
- under 18.5: underweight
- 18.5 to 24.9: healthy range
- 25 to 29.9: overweight
- 30 or more: obese
The tool also gives the healthy weight range for your height by working the formula backwards from a BMI of 18.5 and 24.9.
BMI has clear limits. It cannot tell fat from muscle, so a muscular person can score as overweight. It ignores where fat is carried and does not account for age. The NHS notes that lower thresholds apply to people from Black, Asian and other minority ethnic backgrounds. It is designed for adults, not children. Treat it as a screening guide, not a diagnosis.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Units | Metric (cm, kg) |
| Height | 170 |
| Weight | 68 |
Your BMI: 23.5
| Category | Healthy range |
|---|---|
| Healthy weight for this height | 53.5 – 72 kg |
Tips and common mistakes
Measure height without shoes and weigh yourself at a similar time of day. Treat the number as one piece of information alongside waist size, fitness and how you feel. If your result is outside the healthy range, or you are worried about your weight, speak to a GP, pharmacist or practice nurse. For children, use the NHS child tools instead. General information, not medical advice.
Frequently asked questions
What is a healthy BMI?
The NHS adult healthy range is 18.5 to 24.9. A result under 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese.
Is BMI accurate for athletes?
Not always. BMI cannot tell muscle from fat, so people with a lot of muscle can have a high BMI while carrying little body fat.
Does the calculator work for children?
No. BMI for children and teenagers is read against age and sex charts. This tool is for adults, so use the NHS child tools or speak to a health professional.
Guides that help
- BMI explained: what it tells you and what it doesn't
- Body fat percentage: how it's measured and what's typical