What BMI measures
Body Mass Index (BMI) is a simple number that tells whether a person's body mass is healthy for their height. It is one of the health parameters used to screen for underweight and overweight. BMI does not measure fat directly, but for most people it gives a useful guide.
Key idea
BMI = mass (kg) / height (m)²
Mass is in kilograms and height is in metres. The unit of BMI is kg/m². Remember to square the height, not the mass.
Interpreting the value
The result is compared against standard categories.
| BMI (kg/m²) | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obese |
Example
A student has a mass of 60 kg and a height of 1.6 m. Height squared is 1.6 × 1.6 = 2.56 m². BMI = 60 ÷ 2.56 = 23.4 kg/m². This falls in the 18.5 to 24.9 range, so the student is in the normal category.
Uses and limits
BMI is quick, cheap and needs only a weighing scale and a measuring tape, so it is widely used in Malaysian schools and clinics to spot health risks early. A high BMI is linked to a greater risk of diabetes, hypertension and heart disease, while a very low BMI may signal poor nutrition. However, BMI has limits: a muscular athlete may have a high BMI without excess fat, and it is interpreted differently for children and for different populations. It should be read alongside diet, activity and other checks.
Remember
Always convert height to metres before squaring. A height of 160 cm becomes 1.6 m. Squaring 160 by mistake gives a nonsense answer.