WHO BMI Categories
The World Health Organization sorts adult BMI into bands — underweight, healthy, overweight and three obesity classes. A population screening scale, not a personal verdict.
The WHO adult BMI categories are: underweight below 18.5, healthy weight 18.5–25, overweight 25–30, and obesity in three classes — I (30–35), II (35–40) and III (≥40), in kg/m². The same cut-points apply to men and women. They screen risk across populations; they do not diagnose an individual.
| Category | BMI (kg/m²) |
|---|---|
| Underweight | below 18.5 |
| Healthy weight | 18.5 to below 25 |
| Overweight | 25 to below 30 |
| Obese · class I | 30 to below 35 |
| Obese · class II | 35 to below 40 |
| Obese · class III | 40 and above |
| Category | BMI (kg/m²) |
|---|---|
| Underweight | < 18.5 |
| Healthy weight | 18.5 – 25 |
| Overweight | 25 – 30 |
| Obese · class I | 30 – 35 |
| Obese · class II | 35 – 40 |
| Obese · class III | ≥ 40 |
This is a population screening band, not a diagnosis. The same cut-points apply to adult men and women, ignore muscle and where you carry fat, and read high for very muscular builds. Some Asian populations reach equivalent risk lower (≈23 and 27.5). Read it beside your waist.
A screening scale, not a verdict
These cut-points were drawn to flag risk across populations, where BMI tracks body fat well on average. For any one person the average breaks down: BMI counts a kilogram of muscle exactly like a kilogram of fat, and it can’t see where you carry weight — the single thing most tied to health risk. A number in one band is a prompt to look closer, not a diagnosis.
The obesity classes I–III come from WHO Technical Report Series 894 (splits at 35 and 40), the fuller source behind the shorter public fact sheet.
Where the bands mislead
Muscular builds
Muscle is dense, so athletes often land in “overweight” at a healthy body fat. A high BMI with a normal waist is usually this.
Older adults
Muscle is lost with age, so a “healthy” BMI can hide low muscle and higher fat. Waist and strength say more here.
Asian populations
Equivalent risk arrives lower — roughly 23 for increased and 27.5 for high risk — so the standard bands under-flag it.
A category is a screen. Check it against your waist.
Because BMI can’t see fat distribution, the cheap fix is your waist. Waist-to-height ratio captures central fat directly and is often a better early signal for one person than any BMI band.
Open the waist-to-height calculatorWorld Health Organization (2000). WHO Technical Report Series 894. Cut-points set against population mortality/morbidity risk. Class I/II/III are taken from TRS 894, not the current fact sheet, and are covered by our test suite.
Spot an error in this formula? Report it →
FAQ
What are the WHO BMI categories?
For adults: underweight below 18.5, healthy weight 18.5 to under 25, overweight 25 to under 30, and obesity in three classes — class I 30 to under 35, class II 35 to under 40, class III 40 and above (kg/m²). The same cut-points apply to men and women.
Is a BMI category a diagnosis?
No. The cut-points are a population screening tool — they sort risk across large groups. For one person they can mislead, because BMI can't see muscle, bone or where you carry fat. Read your category beside your waist and how it moves over time, not as a verdict.
Are the BMI cut-points the same for everyone?
The WHO adult cut-points are the same for men and women, but some Asian populations reach equivalent health risk at lower BMI — around 23 for "increased" and 27.5 for "high" risk. Older adults and very muscular builds are also poorly served by the standard bands.
Where do the obesity classes I, II and III come from?
From WHO Technical Report Series 894, which splits obesity at 35 and 40 kg/m² — not the shorter current fact sheet. WIMSTA cites TRS 894 as the primary source and its cut-points are covered by our test suite.
How every threshold is sourced: the method page and the formula registry.