Work out your Body Mass Index (BMI) from height and weight using metric (kg, cm) or US/UK imperial (lb, ft and in). Results are general estimates for informational purposes only—they are not medical advice and do not replace consultation with a doctor or registered dietitian.
Choose metric (kg, cm) or imperial (lb, ft/in)
Enter kg if metric, or lb if imperial
Used when unit system is metric
Used when unit system is imperial
Extra inches; used with feet for imperial
Work out your Body Mass Index (BMI) from height and weight using metric (kg, cm) or US/UK imperial (lb, ft and in). Results are general estimates for informational purposes only—they are not medical advice and do not replace consultation with a doctor or registered dietitian.
Metric: BMI = weight (kg) ÷ height (m)² Imperial: BMI = 703 × weight (lb) ÷ height (in)² WHO adult categories: under 18.5 underweight; 18.5–24.9 normal; 25–29.9 overweight; 30+ obese
Weight 70 kg, height 175 cm Height in metres: 175 ÷ 100 = 1.75 m BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 ≈ 22.9 Category: normal weight range (18.5–24.9)
In metric, divide weight in kilograms by height in metres squared. In imperial, multiply 703 by weight in pounds, then divide by height in inches squared.
WHO adult ranges group BMI into underweight (under 18.5), normal (18.5–24.9), overweight (25–29.9), and obese (30+). They describe population trends, not a diagnosis on their own.
No—pick one system. Enter kg with cm, or lb with ft and in. Mixing units gives a wrong result.
No. BMI is a rough screening tool. It can misclassify muscular athletes, older adults, pregnant people, and some ethnic groups. Treat the number as an estimate and ask a healthcare professional if you need personal advice.
No. This calculator provides general informational estimates only and does not replace consultation with a doctor or registered dietitian.
Body Mass Index (BMI) is one of the most searched health maths topics online. It combines height and weight into a single number so you can compare your result with standard adult categories. The maths is straightforward once you pick either metric or imperial units and stick with that system throughout.
BMI does not measure body fat directly. It is a quick screening ratio used in schools, sports medicine leaflets, and general wellness checks. Because it only uses height and weight, it can overestimate body fat in very muscular people and underestimate risk in some other cases. Treat your result as a rough estimate—not a diagnosis.
Metric: BMI = weight (kg) ÷ [height (m)]² Imperial: BMI = 703 × weight (lb) ÷ [height (in)]² Adult categories (WHO): under 18.5 underweight; 18.5–24.9 normal; 25–29.9 overweight; 30+ obese
A student weighs 70 kg and is 175 cm tall. Convert height to metres: 175 ÷ 100 = 1.75 m. Square it: 1.75 × 1.75 = 3.0625. Divide: 70 ÷ 3.0625 ≈ 22.9. That falls in the normal range (18.5–24.9). In imperial, 154 lb at 5 ft 9 in (69 in total) gives BMI = 703 × 154 ÷ 69² ≈ 22.7—nearly the same answer when conversions are consistent.
Open the BMI Calculator on ProMathTools, choose metric or imperial, then enter your weight and height. For metric, type kilograms and centimetres. For imperial, enter pounds plus feet and inches separately. Press calculate to see your BMI rounded to one decimal, the WHO category, and which formula was applied. If you normally think in stones or metres, convert first using our weight or height converters linked on the page.
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