BMI calculator
Body mass index is weight in kilograms divided by height in metres squared. It is a population-level screen, not a diagnosis: a muscular person can read as "overweight" without a gram of excess fat, and a normal BMI does not rule out risk.
- Category
- Normal weight
- Healthy weight range
- 56.7–76.3 kg
Basis of the calculation
Body mass index is weight divided by height squared. WHO bands: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30 and above obese. BMI does not distinguish muscle from fat, so it can misread athletic builds as overweight.
Rates and thresholds
- Underweight
- below 18.5
- Normal weight
- 18.5 – 24.9
- Overweight
- 25 – 29.9
- Obesity
- 30 and above
How is BMI calculated?
The formula is weight divided by height squared: BMI = kg / m². For example, 70 kg at 1.75 m gives 70 / (1.75 × 1.75) = 22.9 — normal weight. The same formula applies to women and men; children use age-based growth curves instead of adult ranges.
Does BMI work for athletes?
Poorly. Muscle is denser than fat, so a gym-goer can read as overweight on BMI while carrying little body fat. Waist circumference, body-fat percentage or both together say more in that case. BMI serves best when body composition is typical.
What BMI is a health risk?
Risk rises in both directions: below 18.5 associates with malnutrition and bone loss, above 30 with cardiovascular disease and diabetes. The ranges are statistical — individual risk also depends on blood pressure, blood sugar, heredity and lifestyle. See your family doctor about a persistent deviation.
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