Body composition

BMI Calculator

Q: What is a normal BMI for an adult?

According to the WHO, a BMI between 18.5 and 24.9 is considered normal weight for adults over 18, regardless of sex.

Q: Is BMI valid for children?

No. For children under 18, BMI-for-age percentile charts are used, as the body changes significantly during growth.

Q: Why is my BMI high if I exercise a lot?

BMI does not differentiate between muscle and fat. A person with high muscle mass may have an elevated BMI without excess body fat.

Q: How often should I calculate my BMI?

For most adults, checking it every 3–6 months is sufficient, unless your doctor recommends a different frequency.

Calculate your Body Mass Index and find out if your weight is healthy for your height.

Weight (kg)

Height (cm)

What is BMI?

Body Mass Index (BMI) is a measure of body fat based on a person's weight and height. It is used by the World Health Organisation (WHO) as a health indicator for adults over 18. A BMI in the normal range (18.5–24.9) is statistically associated with lower risks of cardiovascular disease, type 2 diabetes and other chronic conditions.

BMI	Category	Interpretation
< 16	Severe underweight
16 – 18.4	Underweight
18.5 – 24.9	Normal weight
25 – 29.9	Overweight
30 – 34.9	Obesity class I
35 – 39.9	Obesity class II
≥ 40	Obesity class III

Source: World Health Organization (WHO), 2000.

How is BMI calculated?

The BMI formula was developed by Belgian statistician Adolphe Quetelet in the 19th century. It is obtained by dividing weight in kilograms by the square of height in metres.

Formula

BMI = Weight (kg) ÷ Height² (m)

BMI = [Weight (lb) ÷ Height² (in)] × 703

⚠️ Limitations

BMI does not distinguish between muscle mass and fat mass, so it can misclassify highly muscular athletes as 'overweight'. It also does not account for fat distribution, age or ethnicity. It should be interpreted alongside other measures such as waist circumference.

FAQ

What is a normal BMI for an adult?

According to the WHO, a BMI between 18.5 and 24.9 is considered normal weight for adults over 18, regardless of sex.

Is BMI valid for children?

No. For children under 18, BMI-for-age percentile charts are used, as the body changes significantly during growth.

Why is my BMI high if I exercise a lot?

BMI does not differentiate between muscle and fat. A person with high muscle mass may have an elevated BMI without excess body fat.

How often should I calculate my BMI?

For most adults, checking it every 3–6 months is sufficient, unless your doctor recommends a different frequency.