What Is BMI?
Body Mass Index relates your weight to your height and is the most widely used screening measure for weight categories. It was developed in the 1830s by Adolphe Quetelet and adopted by the WHO for population statistics.
BMI = weight (kg) ÷ height² (m²) · imperial: 703 × lb ÷ in²
BMI Categories (WHO, Adults)
| BMI | Category |
|---|---|
| below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Worked Example
At 175 cm and 70 kg: BMI = 70 ÷ 1.75² = 22.9 — normal weight. The healthy range for that height spans roughly 56.7 to 76.3 kg.
Where BMI Falls Short
- Muscle vs. fat: BMI cannot tell them apart — muscular athletes often read "overweight" while being very lean.
- Fat distribution: Abdominal fat carries higher health risk than the same BMI with fat stored elsewhere; waist circumference adds useful context.
- Age and ethnicity: Health risk at a given BMI differs across groups; some Asian populations use lower cut-offs (23 for overweight).
BMI is a screening tool, not a diagnosis. Discuss weight-related health questions with a medical professional.