BMI Calculator
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General information only, not medical advice. Talk to a doctor or registered dietitian before making health decisions.
What is BMI?
Body mass index (BMI) compares your weight with your height. It is a quick screening number used by doctors and health organisations to spot weights that may need attention. This calculator is for adults aged 18 and over and accepts metric (cm, kg) or imperial (feet, inches, pounds) units.
How to use it
- Choose your units.
- Enter your height and weight.
- Read your BMI, your WHO category and the weight range that is healthy for your height. The results update as you type.
Formula and source
BMI = weight in kilograms ÷ (height in metres)². For example, 70 kg at 1.75 m gives 70 ÷ 3.0625 = 22.9. The categories follow the World Health Organization adult classification:
- Below 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25 to 29.9: overweight
- 30 to 34.9: obesity class I
- 35 to 39.9: obesity class II
- 40 and above: obesity class III
The healthy weight range shown is the weight that gives a BMI between 18.5 and 24.9 at your height.
Limits of BMI
BMI does not measure body fat, muscle, bone density or where fat is stored. Athletes can have a high BMI while being healthy, and older adults can have a normal BMI with low muscle. Treat the result as a starting point, not a diagnosis, and talk to a doctor or dietitian about your health. Your numbers are processed in your browser and are never uploaded.
Frequently asked questions
What is a healthy BMI?
For adults, the World Health Organization defines a healthy BMI as 18.5 to 24.9. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or more is obesity.
Is BMI accurate for athletes and muscular people?
Not always. BMI cannot tell muscle from fat, so a muscular person can have a high BMI and still be healthy. Waist size and a doctor's assessment give a fuller picture.
Do men and women use the same BMI ranges?
Yes, the WHO adult categories are the same for both. Women usually carry more body fat than men at the same BMI, which is one reason BMI is only a screening tool.
Can I use this calculator for children?
No. Children and teenagers are measured against age- and sex-specific growth charts, so this adult calculator is not suitable. Ask a paediatrician instead.