Calculate your Body Mass Index using kilograms and centimeters — the international standard for BMI measurement, with WHO classification scale and metric formula explained.
International standard formula and WHO classification scale
Our free BMI calculator supports both metric (kg/cm) and imperial (lbs/inches) inputs. Get your instant result and WHO classification.
Open BMI Calculator →The BMI formula in metric units is elegantly simple: BMI = weight in kilograms divided by the square of height in meters. Written mathematically: BMI = kg/m².
To apply it: if you weigh 75 kg and stand 1.78 m tall, your BMI = 75 ÷ (1.78)² = 75 ÷ 3.1684 = 23.7. This places you solidly in the normal weight range (18.5–24.9). If your height is given in centimeters, divide by 100 first to convert to meters (e.g., 178 cm → 1.78 m).
The metric formula is the original and primary standard used globally. The imperial formula (703 × lbs/inches²) is simply a conversion that produces the identical numerical result — the 703 factor accounts for the unit conversion between kilograms and pounds, and meters and inches. The resulting BMI number is always the same regardless of which version you use.
The World Health Organization provides the globally accepted BMI classification system. Unlike some national guidelines, the WHO classification is designed for international use across populations:
Severely underweight: BMI < 16.0
Moderately underweight: BMI 16.0–16.9
Mildly underweight: BMI 17.0–18.4
Normal weight: BMI 18.5–24.9
Pre-obese (overweight): BMI 25.0–29.9
Obese class I: BMI 30.0–34.9
Obese class II: BMI 35.0–39.9
Obese class III (severe): BMI ≥ 40.0
Note that the WHO uses the term "pre-obese" rather than simply "overweight" for BMI 25–29.9, emphasizing that this category represents elevated risk and trajectory toward obesity rather than a neutral status. Many national health agencies use the simpler term "overweight" for the same range.
Here are example BMI calculations to illustrate the metric system in practice:
160 cm, 55 kg: BMI = 55 ÷ (1.60)² = 55 ÷ 2.56 = 21.5 → Normal weight
170 cm, 70 kg: BMI = 70 ÷ (1.70)² = 70 ÷ 2.89 = 24.2 → Normal weight
175 cm, 80 kg: BMI = 80 ÷ (1.75)² = 80 ÷ 3.06 = 26.1 → Pre-obese
180 cm, 90 kg: BMI = 90 ÷ (1.80)² = 90 ÷ 3.24 = 27.8 → Pre-obese
165 cm, 95 kg: BMI = 95 ÷ (1.65)² = 95 ÷ 2.72 = 34.9 → Obese class I
A common question from users switching between metric and imperial units is whether the resulting BMI number will differ. It will not. BMI is a dimensionless ratio — the 703 constant in the imperial formula exists precisely to convert the result to the same scale as the metric formula. Whether you input 75 kg and 1.75 m, or 165 lbs and 69 inches, the calculator will return the same BMI of approximately 24.5.
This mathematical consistency makes BMI universally comparable: a clinical study in Germany, a public health survey in Brazil, or a personal health app in Japan can all reference the same WHO thresholds and communicate meaningful comparisons in a shared language.
One important context for metric BMI users globally is the recognized need for population-specific adjustments. Multiple large-scale epidemiological studies from Asia, particularly from Japan, China, India, and Singapore, have consistently found that Asian populations develop type 2 diabetes, cardiovascular disease, and metabolic syndrome at BMI levels lower than the WHO standard cutoffs of 25.0 and 30.0.
The WHO convened an expert consultation in 2004 that concluded the optimal international cutoffs remain at 25.0 and 30.0, but that countries with predominantly Asian populations should consider additional "action points" at BMI 23.0 (overweight) and 27.5 (obese) for public health interventions. Many Asian national health agencies now use these lower thresholds in their clinical guidelines.
BMI = weight (kg) ÷ [height (m)]². Convert height from cm to m by dividing by 100. Example: 70 kg at 175 cm → 70 ÷ (1.75²) = 70 ÷ 3.0625 = BMI 22.9.
Normal: 18.5–24.9 | Pre-obese: 25.0–29.9 | Obese I: 30.0–34.9 | Obese II: 35.0–39.9 | Obese III: 40.0+. Below 18.5 indicates varying degrees of underweight.
No — the result is identical. The 703 constant in the imperial formula converts units so both calculations produce the same dimensionless BMI number. Choose whichever measurement system you're most familiar with.
Yes. WHO recommends additional action points at BMI 23.0 (overweight) and 27.5 (obese) for Asian populations, who show elevated metabolic risk at lower BMI levels than Western populations. Many Asian national health agencies use these lower thresholds clinically.