How BMI is calculated
BMI is your weight in kilograms divided by the square of your height in metres (kg/m²). The World Health Organization classifies BMI below 18.5 as underweight, 18.5–24.9 as normal, 25–29.9 as overweight and 30 or above as obese. In Japan, the JASSO (Japan Society for the Study of Obesity) standard is stricter: there is no 'overweight' tier, and BMI ≥25 is classified as Obese class 1, ≥30 as class 2, ≥35 as class 3 and ≥40 as class 4. These tighter thresholds reflect higher cardiometabolic risk observed in Asian populations at lower BMI values (source: Examination Committee of Criteria for 'Obesity Disease' in Japan, Japan Society for the Study of Obesity, 2002).
How to use it
Enter your weight and height and your BMI and category appear instantly. Switch the classification standard to WHO (global) or JASSO (Japan) depending on which guidelines you follow. Use the healthy-weight range to see the target weight band for your height.
Frequently asked questions
- Is BMI accurate for everyone?
- No. BMI does not distinguish muscle from fat, so very muscular people may read as overweight. Use it as a general screening tool, not a diagnosis.
- What is a healthy BMI?
- The WHO considers a BMI between 18.5 and 24.9 to be in the healthy range for most adults.
- Does BMI differ by sex or age?
- The standard adult BMI categories are the same for men and women. Different charts are used for children and teens.
- What should I do about my BMI?
- If your BMI is outside the healthy range, consider speaking to a healthcare professional and looking at body fat percentage and waist measurements too.