WHO BMI Classification for Adults

WHO defines overweight in adults as a BMI of 25 or above and obesity as 30 or above. Those two numbers are the whole of the international classification as the WHO fact sheet states it; the finer split into a normal band and three obesity classes comes from the WHO technical reports and is the version reproduced by US agencies.

Category	BMI (kg/m²)
Underweight	below 18.5
Normal weight (healthy weight)	18.5 – 24.9
Overweight, also called pre-obesity	25.0 – 29.9
Obesity class 1	30.0 – 34.9
Obesity class 2	35.0 – 39.9
Obesity class 3, or severe obesity	40.0 and above

What the WHO fact sheet publishes, and what it does not

Worth being precise, because most pages that cite “the WHO classification” are quoting a document they never opened. The current WHO fact sheet on obesity and overweight gives two thresholds for adults, 25 and 30, and nothing else — no underweight line, no class 1, 2 and 3 split. The six-row table above is the classification as carried by the National Library of Medicine and NIDDK, which publish the same 18.5, 25, 30 and 40 boundaries under US names.

So the honest description is: one set of numbers, two vocabularies. WHO’s pre-obesity and the American overweight are the same 25.0 to 29.9. WHO’s class 3 and NIDDK’s severe obesity are the same 40 and above.

The separate cutoffs for Asian populations

This is the part of the classification most often dropped in translation. A WHO expert consultation published in 2004 reviewed evidence that people of Asian descent reach a substantial risk of type 2 diabetes and cardiovascular disease at a BMI below the 25 threshold, and identified four additional public health action points along the BMI continuum:

Action point (kg/m²)	Corresponds to
23.0	increased risk, well inside the international “normal” band
27.5	high risk, below the international obesity line
32.5	higher risk
37.5	highest risk

Two details matter. The consultation did not replace the international classification — it explicitly recommended keeping the WHO cutoffs as the international standard, and offered the action points as a tool for countries deciding their own public health thresholds. And it declined to name a single Asian cutoff, because the observed risk threshold varied between roughly 22 and 25 across the populations reviewed.

At 5 ft 6 in, 23.0 is about 143 lb and 27.5 is about 170 lb, against 155 lb and 186 lb for the standard 25 and 30 lines. That gap of a dozen pounds is the practical size of the adjustment.

Children and teens are not on this table

WHO does not apply the adult bands below age 19. For ages 5 to 19 it defines overweight as BMI-for-age more than 1 standard deviation above the WHO growth reference median and obesity as more than 2 standard deviations above it. Below age 5 the index used is weight-for-height, at 2 and 3 standard deviations. In the United States the same idea is expressed in percentiles rather than standard deviations, which is covered on the BMI chart for children.

Using the classification without over-reading it

The classification is a screening grid built to count populations, and every one of its boundaries is a convention drawn through a continuum. It measures neither body fat nor where fat sits, which is why waist circumference is usually taken alongside it. Find your band, then treat it as the question rather than the answer.

For the weight that each boundary corresponds to at your height, see the BMI chart; for what the first line above the healthy band means in practice, see BMI 25.

This content is informational and does not replace evaluation by a health professional.