The Metric BMI Formula
The metric (SI units) BMI formula is the international standard endorsed by the World Health Organization. It uses kilograms for weight and metres for height:
BMI (metric) formula:
BMI = weight (kg) ÷ height² (m²)
Height conversion: divide cm by 100 to get metres
178 cm ÷ 100 = 1.78 m
The result is expressed in kg/m² (kilograms per square metre). This is the same formula used by the WHO, CDC, and every national health authority worldwide. Source: WHO Obesity Fact Sheet.
Step-by-Step: How to Calculate Metric BMI
Follow these four steps to calculate your BMI using metric units:
- Measure your weight in kilograms (kg). Use a digital scale for accuracy.
- Measure your height in centimetres (cm). Stand straight without shoes.
- Convert height to metres: divide cm by 100. Example: 175 cm ÷ 100 = 1.75 m.
- Apply the formula: divide weight by height squared. Example: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9 kg/m².
On a scientific calculator: enter height in metres → press x² → press ÷ → enter weight in kg → press =. Result is your BMI.
Worked Examples — Real Heights and Weights
| Weight (kg) | Height (cm) | Height (m) | BMI | Category |
|---|---|---|---|---|
| 50 kg | 160 cm | 1.60 m | 19.5 | Normal ✓ |
| 60 kg | 165 cm | 1.65 m | 22.0 | Normal ✓ |
| 70 kg | 170 cm | 1.70 m | 24.2 | Normal ✓ |
| 80 kg | 175 cm | 1.75 m | 26.1 | Overweight |
| 90 kg | 178 cm | 1.78 m | 28.4 | Overweight |
| 100 kg | 180 cm | 1.80 m | 30.9 | Obese Class I |
| 55 kg | 155 cm | 1.55 m | 22.9 | Normal ✓ |
| 45 kg | 162 cm | 1.62 m | 17.1 | Mild Thinness |
WHO BMI Categories (Metric)
| BMI (kg/m²) | Category | Health Risk |
|---|---|---|
| Below 16.0 | Severe Thinness | Very High |
| 16.0 – 16.99 | Moderate Thinness | High |
| 17.0 – 18.49 | Mild Thinness | Moderate |
| 18.5 – 24.99 | Normal Weight ✓ | Lowest |
| 25.0 – 29.99 | Overweight | Increased |
| 30.0 – 34.99 | Obese Class I | Moderate |
| 35.0 – 39.99 | Obese Class II | Severe |
| 40.0 and above | Obese Class III | Very Severe |
Metric vs US Imperial BMI Formula
The only difference between metric and US imperial BMI is the formula constant and input units. The result is the same BMI number:
Metric:
BMI = kg ÷ m²
US Imperial:
BMI = 703 × lbs ÷ inches²
The 703 constant is the conversion factor between the two unit systems. Both formulas produce identical BMI values.
The metric formula is simpler and less error-prone because it requires only one conversion step (cm to m). Our free BMI calculator handles both metric and US units automatically — just select the tab that matches your measurements.
Calculate Your BMI in Metric Units Now
Select "Metric Units" tab — enter height in cm and weight in kg. Instant result with animated gauge, BMI Prime, and healthy weight range.
⚖️ Free Metric BMI Calculator →