Body Mass Index (BMI) Mathematical Formulas
BMI evaluates body mass relative to height squared. Depending on whether you measure in metric units or imperial units, use the respective formula below:
Metric FormulaBMI = Weight (kg) / [ Height (m) ]²
Imperial FormulaBMI = 703 × Weight (lbs) / [ Height (in) ]²
World Health Organization (WHO) BMI Classifications
The table below shows the international BMI cutoff categories established by the World Health Organization for adults aged 20 and older:
| BMI Range | Classification | Health Implication |
|---|---|---|
| Below 18.5 | Underweight | Higher risk of nutritional deficiency and bone density loss. |
| 18.5 – 24.9 | Normal Weight | Lowest statistical risk of cardiovascular and metabolic conditions. |
| 25.0 – 29.9 | Overweight | Moderate risk; increased emphasis on balanced diet and activity. |
| 30.0 or Higher | Obesity | Substantially higher risk for hypertension and type 2 diabetes. |
Step-by-Step BMI Calculation Example
Metric Example (kg & cm)
Consider an individual who is 175 cm (1.75 m) tall and weighs 70 kg:
- Convert height to meters: 175 cm ÷ 100 =
1.75 m. - Square the height: 1.75 × 1.75 =
3.0625. - Divide weight: 70 kg ÷ 3.0625 = 22.86 BMI.
- Result: Normal weight (within 18.5 – 24.9).
Imperial Example (lbs & inches)
Consider an individual who is 5 ft 10 in (70 inches) and weighs 165 lbs:
- Convert height to inches: (5 × 12) + 10 =
70 in. - Square the height: 70 × 70 =
4,900. - Compute with 703 factor: [165 ÷ 4,900] × 703 = 23.67 BMI.
- Result: Normal weight (within 18.5 – 24.9).
Frequently Asked Questions
Common questions and detailed answers regarding calculations and formulas.
Body Mass Index (BMI) is a screening metric that compares your weight to your height. Established by the World Health Organization (WHO), BMI is widely used by clinicians and researchers to categorize individuals into underweight, normal weight, overweight, and obesity ranges.