BMI Calculator
Calculate your Body Mass Index (BMI) from height and weight, then see the matching WHO adult category. Use it as a quick screening number — not a full health diagnosis.
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Measurements convert when you switch units
The formula
BMI divides body mass by height squared. In metric units that is kilograms per metre squared. Imperial inputs are converted first (pounds → kg, inches → m) so the same WHO cutoffs apply. BMI estimates population-level weight status; it does not measure body fat directly.
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 adult category)
How BMI is interpreted
BMI is a screening index. The calculation is simple; the clinical meaning depends on age, sex, ethnicity, muscle mass, and other risk factors.
Adult WHO categories
For most adults, WHO maps BMI to underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), and obese (≥30). Sub-classes of obesity (I–III) are sometimes used in clinical settings.
These cutoffs were designed for population surveillance. An individual with high muscle mass can land in the “overweight” band with relatively low body fat.
Asian and other ethnic cutoffs
Some regional guidance (including WHO Western Pacific discussions) uses lower action points such as BMI ≥23 for increased risk in Asian populations, reflecting higher cardiometabolic risk at a given BMI. Always follow the guidance your clinician uses for you.
Children and teens
Under 18, BMI must be read against age- and sex-specific growth-chart percentiles (CDC or WHO), not the adult bands shown on this page. A “normal adult” number can be inappropriate for a growing child.
What BMI misses
BMI ignores fat distribution, fitness, bone density, and edema. Pair it with waist measures, body-fat estimates, labs, and clinical judgment when decisions matter.
Interesting facts
Invented as the Quetelet Index
Belgian statistician Adolphe Quetelet proposed the weight/height² relationship in the 1830s. Ancel Keys popularized the name “body mass index” in the 1970s.
Different cutoffs in Asia
WHO Western Pacific Region discussions recommend considering overweight action points near BMI ≥23 for many Asian populations because health risks can rise at lower BMI values.
Not ideal for athletes
A rugby forward or bodybuilder can have BMI over 30 while carrying low body fat — muscle is denser than fat, so weight/height² overstates adiposity.
Used worldwide for screening
BMI remains the most widely used population weight metric because it needs only height and weight — no scanners or calipers.
Children use percentiles
For under-18s, CDC and WHO growth charts convert BMI into age- and sex-specific percentiles rather than adult 18.5–24.9 cutoffs.
Frequently asked questions
Divide weight in kilograms by height in metres squared. This calculator also accepts imperial units and converts them automatically before applying WHO adult categories.
It is a useful screen for most adults but can overestimate fatness in muscular people and underestimate risk in older adults who have lost muscle. It is not a diagnosis.
For most adults, WHO defines normal weight as BMI 18.5–24.9, overweight as 25–29.9, and obese as 30 or above. Regional or clinical guidelines may differ.
Either works — use the unit toggle. The underlying formula is always kg/m² after conversion.
No. BMI is a screening indicator. See a qualified clinician for personal assessment, especially if you have other risk factors.
Not with adult cutoffs. Children and teens need age- and sex-specific percentile charts from CDC or WHO.
References
- Obesity and overweight — fact sheet Adult BMI category definitions used internationally.
- About adult BMI How BMI categories are used in US public-health practice.
- BMI-for-age growth charts Pediatric interpretation uses percentiles, not adult cutoffs.
- Appropriate body-mass index for Asian populations Context for lower BMI action points in some Asian populations.