How BMI is calculated
Body mass index is your weight in kilograms divided by your height in meters squared. For someone who weighs 70 kg and is 1.75 m tall, that is 70 divided by 3.06, a BMI of about 22.9. In pounds and inches, multiply weight in pounds by 703 and divide by height in inches squared.
BMI categories for adults
| BMI | WHO category | Asian cut offs |
|---|---|---|
| Below 18.5 | Underweight | Below 18.5 |
| 18.5 to 24.9 | Healthy weight | 18.5 to 22.9 |
| 25 to 29.9 | Overweight | 23 to 27.4 |
| 30 to 34.9 | Obesity class 1 | 27.5 and above |
| 35 to 39.9 | Obesity class 2 | |
| 40 and above | Obesity class 3 |
The World Health Organization suggests lower cut offs for people of Asian heritage, because health risks such as type 2 diabetes tend to rise at a lower BMI. Tick the box in the calculator to use them.
What BMI can and can't tell you
BMI is a quick, free screening tool that works well across large groups of people, which is why doctors and health agencies use it. But it has real limits for individuals. It doesn't separate muscle from fat, so athletes can score as overweight. It doesn't show where fat sits, and fat around the waist carries more risk than fat on the hips. It is also less reliable for older adults, who may have less muscle at the same BMI.
What to do with your result
If your BMI is outside the healthy range, it's a prompt to look closer rather than a verdict. Talk to a doctor, and use the calorie calculator and weight loss calculator to plan realistic, gradual changes. The ideal weight calculator compares several formulas for your height.
Sources: World Health Organization BMI classification; WHO Expert Consultation on BMI in Asian populations, The Lancet 2004; NHS and CDC adult BMI guidance.
