How it is calculated
BMI is your weight in kilograms divided by the square of your height in metres:
BMI = weight (kg) ÷ height² (m)The result is compared with the WHO adult classification:
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25 – 29.9 | Overweight |
| 30 – 34.9 | Obesity class I |
| 35 – 39.9 | Obesity class II |
| 40 and above | Obesity class III |
Your healthy weight range is the weight that keeps BMI between 18.5 and 24.9 for your height.
Worked example
Someone weighing 80 kg at 175 cm: height in metres is 1.75, squared 3.0625. BMI = 80 ÷ 3.0625 = 26.1, which is "overweight". The healthy range for that height is roughly 56.7–76.3 kg.
Frequently asked questions
Is BMI accurate for everyone?
It is a quick population-level screen and does not separate muscle from fat. Very muscular people can show as "overweight" while being healthy, so pair it with a waist measurement.
Can I use it for children?
No. Under 18, BMI is read against age- and sex-specific growth charts, best assessed by a paediatrician.
Are the categories different for men and women?
The WHO adult categories are the same for both sexes, although body-fat percentage at the same BMI usually differs.
What is my ideal weight?
There is no single number — the calculator shows a healthy range between BMI 18.5 and 24.9 for your height.
Are cut-offs different for Asian populations?
Some health bodies use lower thresholds for some Asian populations (e.g. 23 for overweight) because risks rise at a lower BMI.