What is BMI?
Body Mass Index (BMI) is a simple number calculated from your height and weight. You can calculate yours in seconds using our free body mass index (BMI) calculator which aligns with standard WHO categories and is used as a screening tool to identify whether a person is underweight, normal weight, overweight or obese. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is now the most widely used population health metric globally.
BMI does not directly measure body fat, but it correlates reasonably well with direct body fat measurements for most people and is far simpler and cheaper to calculate.
The BMI Formula
Example: 70 kg ÷ (1.70 m)² = 70 ÷ 2.89 = 24.2
Example: 154 lbs ÷ (67 in)² × 703 = 24.1
WHO BMI Categories
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk of malnutrition |
| 18.5 – 24.9 | Normal weight | Lowest health risk |
| 25.0 – 29.9 | Overweight | Moderate increased risk |
| 30.0 – 34.9 | Obese Class I | High risk |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40+ | Obese Class III | Extremely high risk |
💡 For South Asian adults (including Indians), the WHO recommends lower thresholds: overweight at BMI ≥23 and obese at BMI ≥27.5, as health risks appear at lower BMI compared to Western populations.
Key Limitations of BMI
- Muscle mass: Athletes may have high BMI despite low body fat — muscle is denser than fat.
- Age: Older adults carry more fat at the same BMI compared to younger people.
- Sex differences: Women naturally carry more body fat than men at the same BMI.
- Ethnicity: Risk thresholds vary across ethnic groups.
- Fat distribution: Where fat is stored matters — abdominal fat is more dangerous than fat elsewhere.
⚠️ BMI is a screening tool only, not a diagnosis. Always consult a qualified healthcare professional for a complete health assessment.
💪 Calculate your BMI instantly — metric or imperial
Open BMI Calculator →🔬 External Scientific References & Authoritative Sources
- World Health Organization (WHO) — Body Mass Index (BMI) & Global Nutritional Health Benchmarks.
- National Institutes of Health (NIH) — Clinical Energy Expenditure & Gestational Calculation Research.
- Centers for Disease Control and Prevention (CDC) — Growth Charts, Weight Management & Dietary Guidelines.