How to use the BMI Calculator
- Enter your height in centimeters and your weight in kilograms. Your BMI and weight category show up right away. If you use feet, inches or pounds, convert first (see the FAQ below).
- Look at the colored bar to see which band your BMI falls in.
- Check the Healthy weight range. It's the range of weights that gives a BMI of 18.5–22.9 at your height. Use it as a guide when you set a goal weight.
- If you like, choose your sex and enter your waist circumference to check for abdominal obesity as well.
BMI formula and a worked example
BMI (body mass index) is your weight divided by the square of your height in meters.
BMI = weight (kg) ÷ height (m) ÷ height (m)
Say you're 170 cm tall and weigh 65 kg. That's 65 ÷ (1.7 × 1.7) = 65 ÷ 2.89 = about 22.5, which counts as normal on both scales. At the same height, 75 kg gives 75 ÷ 2.89 = about 26.0. The WHO calls that overweight, and the Asia-Pacific scale calls it class 1 obesity.
In imperial units the formula is BMI = 703 × weight (lb) ÷ height (in)². This calculator takes metric values only, so convert inches and pounds before you enter them.
BMI categories: WHO vs. Asia-Pacific cutoffs
The calculator gives you two classifications. The main label uses the Asia-Pacific cutoffs adopted by the Korean Society for the Study of Obesity (2022 guidelines). The WHO category card uses the international standard that health services in the US, UK, Canada and Australia generally use for adults.
| BMI | Asia-Pacific (main label) | WHO (international) |
|---|---|---|
| Under 18.5 | Underweight | Underweight |
| 18.5 – 22.9 | Normal | Normal |
| 23 – 24.9 | Pre-obese | Normal |
| 25 – 29.9 | Class 1 obesity | Overweight (pre-obese) |
| 30 – 34.9 | Class 2 obesity | Obese class I |
| 35 and over | Class 3 obesity (severe) | Obese class II (class III from 40) |
The Asia-Pacific scale is stricter because people of Asian descent tend to carry more abdominal fat at the same BMI and face a higher risk of metabolic conditions like type 2 diabetes and high blood pressure. Some Western guidelines recognize this too. In the UK, for example, NICE advises lower thresholds for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background. If neither of these applies to you, go by the WHO category.
The healthy weight range card follows the stricter scale (BMI 18.5–22.9). Under the WHO scale, the upper limit of the normal range is a bit higher, at a BMI just under 25.
Waist circumference and abdominal obesity
You can have a normal BMI and still carry a lot of fat around your middle. This calculator flags abdominal obesity at a waist of 90 cm or more for men and 85 cm or more for women. Those are the Korean Society for the Study of Obesity cutoffs.
Other guidelines draw the line in other places:
- International Diabetes Federation (people of European descent): 94 cm (about 37 in) or more for men, 80 cm (about 31.5 in) or more for women.
- US NIH / NHLBI: over 102 cm (40 in) for men, over 88 cm (35 in) for women.
- Waist-to-height ratio: the NHS and NICE suggest keeping your waist below half your height.
For an accurate reading, breathe out normally and wrap a tape measure level around your body, midway between your lowest rib and the top of your hip bone (the iliac crest). Measure on bare skin, not over clothes.
Limits of BMI: when to be careful
- Very muscular people: athletes and others with a lot of muscle can get a high BMI even with little body fat.
- Older adults: as muscle is lost with age, BMI can look normal even when body fat is high.
- Pregnant women, children and teens: the adult categories don't apply. Children and teenagers are assessed with BMI-for-age percentiles on sex-specific growth charts, such as the CDC charts in the US or the UK-WHO charts in Britain.
To know your actual body composition, check your body fat percentage as well, for example with a body composition scale or a scan offered by a clinic or gym. If you need to change weight units, try the weight converter.