What is BMI?
Body mass index (BMI) dates back to the 19th-century Belgian statistician Adolphe Quetelet. It's calculated as weight (kg) ÷ height (m)², or 703 × pounds ÷ inches² if you use US units. A 5'7" adult who weighs 160 lb has a BMI of about 25. Because it takes seconds and needs no equipment, doctors and public health surveys use it everywhere.
What's a healthy BMI?
| Category | CDC/WHO adult range |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5–24.9 |
| Overweight | 25–29.9 |
| Obesity | 30 and above |
Some groups use lower cutoffs. A WHO expert panel (2004) noted that many Asian populations carry more body fat and diabetes risk at the same BMI, so Korea, for example, defines obesity as 25 or higher.
Why BMI isn't the whole story
BMI can't tell muscle from fat, so a muscular athlete may read as "overweight" while an older adult with little muscle may look "normal." That's why clinicians also check waist circumference (in the US, above 40 in for men or 35 in for women signals higher risk). Belly fat is closely tied to metabolic syndrome and type 2 diabetes.
This article is general health information and is not a substitute for diagnosis or treatment. If symptoms persist, see a doctor.
FAQ
- Is a BMI of 26 bad?
- It falls in the overweight range, but your doctor will also look at waist size, blood pressure, blood sugar and fitness before drawing conclusions.
- Do kids use the same chart?
- No. For children and teens, BMI is compared with age- and sex-specific percentiles.
Sources reviewed: 2026-10-25
References
- World Health Organization. (2000). Obesity: Preventing and managing the global epidemic (WHO Technical Report Series 894). WHO.
- WHO Expert Consultation. (2004). Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet, 363(9403), 157–163.
- 대한비만학회. (2022). 비만 진료지침 2022(8판). 대한비만학회.