What is BMI?
Body Mass Index (BMI) is a numerical value derived from a person's weight and height. It's used as a screening tool to categorize weight status and potential health risks.
Formula: BMI = weight (kg) ÷ height² (m²)
Example: A person weighing 70kg at 1.75m height: BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9
BMI categories (WHO standard)
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk of nutritional deficiency |
| 18.5 – 24.9 | Normal weight | Low risk |
| 25.0 – 29.9 | Overweight | Increased risk |
| 30.0 – 34.9 | Obese Class I | High risk |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40.0 and above | Obese Class III | Extremely high risk |
Healthy weight ranges by height
| Height | Healthy weight range (BMI 18.5–24.9) |
|---|---|
| 155 cm | 44 – 60 kg |
| 160 cm | 47 – 64 kg |
| 165 cm | 50 – 68 kg |
| 170 cm | 54 – 72 kg |
| 175 cm | 57 – 76 kg |
| 180 cm | 60 – 81 kg |
| 185 cm | 63 – 85 kg |
Limitations of BMI
BMI is a useful population-level screening tool but has significant limitations for individuals:
Overestimates fatness in:
- Athletes and muscular people (muscle is denser than fat)
- People with large frame/bone structure
Underestimates fatness in:
- Elderly people who have lost muscle mass
- People with very low muscle mass
Does not account for:
- Where fat is distributed (belly fat is more dangerous than hip fat)
- Age (healthy BMI ranges differ for children and elderly)
- Ethnicity (Asian populations show higher health risks at lower BMI values)
BMI vs other measurements
- Waist circumference: Better predictor of cardiovascular risk than BMI
- Waist-to-hip ratio: Measures fat distribution
- Body fat percentage: Most accurate but requires special equipment
- BMI Prime: BMI divided by 25 (upper limit of normal) — values above 1.0 indicate overweight
How to calculate BMI free
- Go to BMI Calculator
- Enter your weight and height (metric or imperial)
- See your BMI, category, and healthy weight range for your height
- Calculate target weight to reach a goal BMI
Disclaimer: BMI is a screening tool, not a diagnosis. Consult a healthcare professional for personalized health advice.