BMI Calculator

Enter your height and weight to get your body mass index (BMI) and see which World Health Organization category it falls into.

How the calculation works

Body mass index dates back to the 19th-century Belgian statistician Adolphe Quetelet, which is why it is also called the Quetelet index. The formula is BMI = weight (kg) / height (m)². The calculator converts your height from centimetres to metres and rounds the result to one decimal place.

Categories follow the WHO classification for adults: below 18.5 underweight; 18.5–24.9 normal; 25–29.9 overweight; 30–34.9 obesity class I; 35–39.9 class II; 40 and above class III. The cards under the result highlight the band you are in. The same cut-offs are used by the CDC and NIH in the US.

Inputs are height in centimetres (100–230) and weight in kilograms (30–200, in 0.5 kg steps). If you think in imperial units, convert first: 1 inch = 2.54 cm and 1 lb = 0.4536 kg. BMI is a screening measure for adults; it does not measure body fat directly and is not a diagnosis.

Worked example

Default values: 175 cm (about 5 ft 9 in) and 70 kg (about 154 lb). BMI = 70 / 1.75² = 70 / 3.0625 ≈ 22.9, which is in the normal range. At that height, a BMI of 18.5–24.9 corresponds to roughly 56.7–76.3 kg (125–168 lb).

Things to keep in mind

• Muscular athletes can score as overweight without excess fat, while older adults who have lost muscle may look healthier on BMI than they are.
• Add a waist measurement: WHO links increased risk to a waist above 94 cm (37 in) in men and 80 cm (31.5 in) in women, and substantially increased risk above 102 cm (40 in) and 88 cm (35 in).
• Adult cut-offs do not apply to children and teens; their BMI is read against age- and sex-specific growth percentiles.
• BMI is not used to judge weight during pregnancy; use pre-pregnancy BMI and your clinician's guidance.
• A WHO expert consultation suggested lower action points for Asian populations: increased risk from 23 and high risk from 27.5.