The BMI formula
BMI = weight (kg) ÷ height (m)2 Imperial: BMI = 703 × weight (lb) ÷ height (in)2The 703 is not magic — it is the unit-conversion factor that makes the imperial version give the same result as the metric one.
Worked example
A person 175 cm tall weighing 72 kg: BMI = 72 ÷ 1.75² = 23.5, inside the healthy 18.5–24.9 band. For that height, the healthy weight range is about 56.7 kg to 76.3 kg.
Honest limitations of BMI
BMI is a population screening number, not a diagnosis. It cannot tell muscle from fat, so muscular athletes often score "overweight" incorrectly; it is not designed for children (who need BMI-for-age percentiles) and it does not account for pregnancy or where fat is carried. Use it as a starting point for a conversation with a health professional, never as a verdict.
Frequently asked questions
Is BMI different for men and women?
The adult formula and the standard categories are the same for both sexes. Body composition differs on average, which is one reason BMI is a screening tool, not a diagnosis.
What BMI is considered healthy?
For adults, 18.5 to 24.9 is the standard healthy range used by the WHO and most health services.
Why does my BMI say overweight when I exercise a lot?
Muscle is denser than fat. BMI uses only height and weight, so it can overestimate body fat in muscular people.
Should children use this calculator?
No — children and teens need BMI-for-age percentiles that account for growth. Ask a pediatric professional instead.