Calculate your Body Mass Index to assess whether your weight is in a healthy range.
A BMI calculator computes your Body Mass Index to classify your weight relative to your height. The NHS and WHO use this as a general health screening tool:
For example, a person weighing 70 kg (11 stone) and 1.75 m (5 ft 9 in) tall has a BMI of 22.86 (Normal). The NHS recommends aiming for a BMI between 18.5 and 24.9. Check the NHS BMI calculator for additional guidance.
| Category | BMI Range |
|---|---|
| Underweight | < 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obesity Class I | 30.0 – 34.9 |
| Obesity Class II | 35.0 – 39.9 |
| Obesity Class III | ≥ 40.0 |
A normal BMI ranges from 18.5 to 24.9 according to the NHS and WHO. Below 18.5 is underweight, 25-29.9 is overweight, and 30 or above is classified as obese.
BMI is calculated by dividing your weight in kilograms by the square of your height in metres: BMI = weight(kg) / height(m)^2. For stone and pounds, convert to kg first (1 stone = 6.35 kg, 1 lb = 0.454 kg).
BMI is a useful screening tool but has limitations. It does not distinguish between muscle and fat, so athletes may have a high BMI despite low body fat. The NHS notes it may be less accurate for certain ethnic groups, elderly people, and pregnant women.
The NHS recommends a BMI between 18.5 and 24.9 for most adults. People of Black African, African-Caribbean, and South Asian heritage may have a higher risk of health problems at a lower BMI, with a recommended range of 18.5-23.