BMI Calculator
Calculate your Body Mass Index (BMI) instantly. Enter your weight and height to see where you fall on the WHO weight categories.
Calculate
Calculate
Measurements convert when you switch units
The formula
Body Mass Index (BMI) is a simple measure using your height and weight to estimate body fat. Healthcare providers worldwide use it as a screening tool — though it does not directly measure body fat and may misclassify very muscular people.
Worked example
- Convert 175 cm to 1.75 m
- Square 1.75 → 3.0625
- Divide 70 kg by 3.0625 = 22.9
Result: 22.9 — Normal weight (WHO category)
How to interpret BMI
BMI is a screening index. The math is simple, but clinical meaning depends on age, sex, ethnicity, muscle mass, and other risk factors.
WHO adult categories
For most adults, WHO groups BMI as underweight (<18.5), normal weight (18.5–24.9), overweight (25–29.9), and obesity (≥30). Clinics sometimes subdivide obesity into classes I–III.
These cutoffs were designed for population health monitoring. Someone with high muscle mass can land in the overweight range while carrying relatively little body fat.
Asian and other ethnic cutoffs
Some regional guidelines (including WHO Western Pacific) use lower action thresholds such as BMI ≥23 for Asian populations because cardiometabolic risk can rise earlier. Follow the advice your clinician uses for you.
Children and teens
Under age 18, BMI should be read against age- and sex-specific percentiles on growth charts (CDC or WHO), not against the adult bands on this page. An “adult normal” number can mislead for a growing child.
What BMI does not show
BMI ignores fat distribution, fitness, bone density, and fluid retention. Important decisions should add waist circumference, body-fat estimates, labs, and clinical judgment.
Interesting facts
Invented by a Belgian statistician
Adolphe Quetelet created the "Quetelet Index" in the 1830s, long before it was renamed BMI in the 1970s by Ancel Keys.
Different cutoffs in Asia
WHO Western Pacific Region recommends overweight at BMI ≥ 23 for Asian populations, reflecting higher health risks at lower BMI values.
Not ideal for athletes
A rugby forward or bodybuilder can have a BMI over 30 while carrying low body fat — muscle weighs more than fat per volume.
Used in 200+ countries
BMI remains the most widely used population-level weight screening metric because it requires only height and weight — no special equipment.
Frequently asked questions
BMI is a useful screening tool for most adults but can overestimate fatness in muscular people and underestimate it in elderly individuals who have lost muscle mass.
For most adults, WHO defines normal weight as BMI 18.5–24.9, overweight as 25–29.9, and obese as 30 or above.
Either works — this calculator converts automatically. Use whichever units you normally measure in.
No. BMI is a screening indicator, not a diagnosis. Consult a healthcare provider for a full assessment.
References
- Obesity and overweight — fact sheet Adult BMI category cut-offs used for population screening.
- About adult BMI How BMI is calculated and interpreted for adults.