BMI calculator
What is a Bmi Calculator?
Body Mass Index (BMI) is a simple screening measure that relates weight to height. Health organisations use it to classify adults into weight categories and to flag possible health risks at population level. This calculator works with kilograms and centimetres or with pounds, feet and inches, and shows the healthy weight range for your height.
How to use it
- Choose metric or imperial units.
- Enter your height and weight.
- Read your BMI, the WHO category and the weight range that corresponds to a healthy BMI at your height.
The formula
Metric: BMI = weight (kg) / height (m)². Imperial: BMI = 703 × weight (lb) / height (in)². For example, 70 kg at 1.75 m gives 70 / 3.0625 = 22.9, which is in the normal range.
WHO categories for adults
- Below 18.5: underweight
- 18.5 to 24.9: normal weight
- 25.0 to 29.9: overweight
- 30.0 and above: obesity (class I 30 to 34.9, class II 35 to 39.9, class III 40 and above)
For 1.75 m, the healthy range of 18.5 to 24.9 corresponds to about 56.7 kg to 76.3 kg.
Limitations
- BMI does not distinguish muscle from fat, so athletes can show a high BMI while being lean.
- It does not show where fat is stored; waist circumference adds useful information.
- Children and teenagers need age- and sex-specific percentile charts, not adult categories.
- Some health bodies use lower cut-offs for people of Asian descent.
BMI is a screening tool, not a diagnosis. Discuss results with a healthcare professional.
Frequently Asked Questions
How is BMI calculated?
Divide weight in kilograms by height in metres squared. In imperial units, multiply weight in pounds by 703 and divide by height in inches squared.
What is a healthy BMI?
For adults, the WHO considers 18.5 to 24.9 a normal weight range.
Is BMI accurate for athletes?
Not always. Muscle is dense, so muscular people can have a high BMI without excess body fat.
Can children use this calculator?
Adult categories do not apply to children and teenagers. They need BMI-for-age percentile charts.