How BMI is calculated
BMI (body mass index) is your weight divided by the square of your height.
BMI = weight (kg) ÷ height (m)²
Example: at 170 cm and 65 kg, 65 ÷ (1.7 × 1.7) = 22.5. The category is based on the value rounded to one decimal place.
BMI categories
| Korean (KSSO) | WHO | |
|---|---|---|
| 1 | Underweight Below 18.5 | Underweight Below 18.5 |
| 2 | Normal 18.5 – 22.9 | Normal 18.5 – 24.9 |
| 3 | Pre-obesity 23.0 – 24.9 | Overweight 25.0 – 29.9 |
| 4 | Obesity stage 1 25.0 – 29.9 | Obesity class I 30.0 – 34.9 |
| 5 | Obesity stage 2 30.0 – 34.9 | Obesity class II 35.0 – 39.9 |
| 6 | Obesity stage 3 35.0 and above | Obesity class III 40.0 and above |
At the same BMI, Asian people tend to have higher body fat and a higher risk of metabolic disease than Western people, so Korea uses a lower cutoff than the WHO (obesity from 25).
Healthy weight by height
This table converts the WHO healthy range (BMI 18.5–24.9) into weight for each height.
| Height | Healthy weight (BMI 18.5–24.9) | Obesity starts (BMI 30) |
|---|---|---|
| 150cm | 41.6 – 56.0 kg | 67.5 kg |
| 155cm | 44.4 – 59.8 kg | 72.1 kg |
| 160cm | 47.4 – 63.7 kg | 76.8 kg |
| 165cm | 50.4 – 67.8 kg | 81.7 kg |
| 170cm | 53.5 – 72.0 kg | 86.7 kg |
| 175cm | 56.7 – 76.3 kg | 91.9 kg |
| 180cm | 59.9 – 80.7 kg | 97.2 kg |
| 185cm | 63.3 – 85.2 kg | 102.7 kg |
| 190cm | 66.8 – 89.9 kg | 108.3 kg |
Things to keep in mind
- Very muscular people can have a high BMI even with little body fat.
- Abdominal obesity is checked separately by waist size. The Korean Society for the Study of Obesity (KSSO) defines it as 90 cm or more for men and 85 cm or more for women.
- Children and teens under 19 are assessed with sex- and age-specific growth chart percentiles. BMI is also interpreted differently for pregnant women and older adults.
Standards and sources
- KSSO clinical practice guidelines for obesity: diagnostic criteria for adult obesity (BMI and waist circumference)
- WHO adult BMI classification · WHO European Health Information Gateway
Last reviewed October 7, 2026
Frequently asked questions
What is a healthy BMI range?
It's 18.5–24.9 under the WHO standard and 18.5–22.9 under the Korean Society for the Study of Obesity (KSSO) standard. The KSSO standard is widely used for Korean adults.
Why do the Korean and WHO standards differ?
At the same BMI, Asian people tend to have higher body fat and a higher risk of metabolic diseases such as diabetes, so a lower cutoff is used.
Is a BMI of 25 obese?
Under the KSSO standard, stage 1 obesity starts at 25. Under the WHO standard, 25–29.9 is overweight.
Can children and teenagers use this?
No. Anyone under 19 should be assessed with BMI percentiles on sex- and age-specific growth charts, so this calculator's result shouldn't be used as is.
What if I'm very muscular?
BMI can't tell muscle from fat, so a lot of muscle can push you into an obese category. Check your waist size or a body composition test as well.