What Is BMI?
Body Mass Index (BMI) is a simple numerical measure that uses your weight and height to estimate whether you are underweight, at a healthy weight, overweight, or obese. Developed by Adolphe Quetelet in the 1830s, BMI remains one of the most widely used screening tools in healthcare worldwide.
The BMI Formula
BMI = weight (kg) ÷ height (m)²
For example, if you weigh 70 kg and are 1.75 m tall: BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.86.
WHO Classification Categories
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese Class I |
| 35.0 – 39.9 | Obese Class II |
| 40.0+ | Obese Class III |
BMI Limitations
BMI is a useful screening tool but has known limitations. It does not distinguish between muscle and fat mass, so athletes with high muscle mass may have a high BMI without excess body fat. It also does not account for fat distribution, age, sex, or ethnicity — all of which can affect health risk. Always discuss BMI results with a healthcare provider for a complete assessment.
Healthy Weight Range
This calculator shows your healthy weight range based on the normal BMI category (18.5–24.9). For a given height, the minimum healthy weight is 18.5 × height² and the maximum is 24.9 × height². This range gives you a target to work toward if your current BMI falls outside the normal category.