Checked 15 October 2026. What was checked. How these pages are maintained.
BMI formula
BMI = weight (kg) ÷ height (m)². In US units: BMI = 703 × weight (lb) ÷ height (in)². Adult categories used by many health agencies: underweight under 18.5, healthy 18.5–24.9, overweight 25–29.9, obesity 30 and above.
BMI does not measure body fat, muscle, or health. Athletes can land in “overweight” with low fat. It is a screening number, not a diagnosis. Talk to a clinician about your own case.
Worked example
A person 170 cm and 70 kg has BMI 24.2, in the standard adult “healthy” range (18.5–24.9). At 6 ft 0 in and 200 lb, BMI is about 27.1, in the “overweight” band on that same chart.
BMI does not see muscle, bone, or where fat sits. Athletes, older adults, and pregnancy make the chart a poor fit. It is a screening number, not a diagnosis. Not medical advice.
One number from height and weight
BMI is weight in kilograms divided by height in metres squared. At 162 cm and 58 kg, height is 1.62 m, 1.62 × 1.62 = 2.6244, and 58 ÷ 2.6244 = 22.1. The adult bands on this page are under 18.5 underweight, 18.5 to 24.9 a healthy-weight range, 25 to 29.9 overweight, and 30 and above an obesity range. 22.1 sits in the healthy-weight band on that chart. The US path is 703 × pounds ÷ inches squared, and it is the same index after the unit conversion. A person who is 5 ft 7 in and 154 lb is in the same neighbourhood. Use one unit system at a time. Mixing centimetres with pounds does not get converted unless you switch the unit control, which shows the other boxes.
Children do not use these adult cutoffs. They are compared with age-and-sex percentiles. This page has no age box and no percentile. It is for adults.
What the chart cannot see
Muscle, bone, pregnancy, and where fat sits are invisible to a ratio of weight and height. A muscular adult can land in the overweight band with relatively little fat. An older adult can land in the healthy band with less muscle than the chart assumes. Some population guides use lower cutoffs than the WHO adult split this page uses. None of that is a diagnosis, and a single BMI is a weak reason to overhaul eating or training. The calorie calculator is a separate estimate of intake, not a correction to BMI. Take a result you are worried about to a clinician.
Common questions
Is BMI different for children?
Yes. Children use age-and-sex percentiles, not these adult cutoffs. This page is for adults.
Why do some charts start obesity at 30?
That is the common WHO adult split. Some Asian-population guides use lower cutoffs.