BMI by height and weight

What the categories are

The WHO thresholds are: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30 and above obese. They are the same for adult men and women and do not adjust for age.

The boundaries are conventions drawn on a continuum, not cliffs. A BMI of 24.9 and one of 25.1 describe near-identical bodies, so treating the category change as meaningful reads more into the number than it contains.

What BMI does not measure

BMI is weight divided by height squared. It has no way to distinguish muscle from fat, so a muscular athlete routinely lands in the "overweight" band while carrying very little fat. It also says nothing about where fat is distributed, and abdominal fat carries meaningfully more health risk than the same mass elsewhere.

It was designed by Adolphe Quetelet in the 1830s to describe populations, not to assess individuals. It is still good at the first job and was never intended for the second.

Where it is least reliable

BMI is least useful for athletes and anyone with high muscle mass, for older adults who have lost muscle while keeping weight steady, for people well outside average height in either direction, and across ethnic groups — the risk thresholds genuinely differ, and several health bodies use a lower cutoff for South Asian populations.

Waist circumference and waist-to-height ratio are better single numbers for an individual. Under half your height is the usual guide.

Common questions