What are the obesity classes?

The WHO divides obesity into three classes by BMI. On the WHO international scale, class 1 is 30.0–34.9, class 2 is 35.0–39.9 and class 3 is 40.0 and above. Class 3 is what older writing called morbid obesity. Where a national standard adopts the Asian obesity line of 25.0 instead of 30.0, all three boundaries shift down by five points.

What BMI is class 3 obesity?

40.0 or above on the WHO international scale, where obesity itself begins at 30.0. Where the obesity line is 25.0 — Korea's KSSO guidelines and Japan's JASSO classification — class III begins at 35.0 instead. The class structure is identical; the whole ladder has simply moved.

Is "morbid obesity" still used?

It has largely been replaced by "class 3 obesity" in clinical writing, because the older term was felt to be stigmatising. The definition did not change: a BMI of 40.0 or above, or 35.0 or above together with an obesity-related condition such as type 2 diabetes, hypertension or obstructive sleep apnoea.

Do obesity classes change for Asian populations?

The boundaries do, and not every Asian standard subdivides obesity at all. Korea's KSSO runs class I 25.0–29.9, class II 30.0–34.9 and class III 35.0 or above; Japan's JASSO uses the same 25 / 30 / 35 boundaries across four classes, merging 3 and 4 into high-degree obesity. By contrast China's WS/T 428 defines obesity from 28.0 without subdividing it, Hong Kong's Department of Health stops at obese I and II, and the ADA's 2026 Asian criteria set a single obesity line at 27.5.

Obesity Classes

Three classes, one threshold — and a ladder that shifts five points sideways the moment you cross the Pacific.

On the WHO international scale, obesity begins at BMI 30.0 and is divided into class 1 (30.0–34.9), class 2 (35.0–39.9) and class 3 (40.0 and above) — the band the CDC now calls severe obesity and older writing called morbid obesity. Where a national standard adopts the Asian obesity line of 25.0, the entire ladder moves down five points: class 1 from 25.0, class 2 from 30.0, class 3 from 35.0. The structure is identical. Only its position changes.

The WHO obesity classes

This is the ladder as the WHO and the CDC publish it. The sub-division matters clinically because the three classes carry materially different risk and different treatment options — which is why flattening them all into "obese" loses information.

BMI range	Classification
< 18.5	Underweight
18.5 – < 25	Normal weight
25 – < 30	Overweight
30 – < 35	Obese class I
35 – < 40	Obese class II
≥ 40	Obese class III (severe obesity)

Source: WHO Expert Consultation, Lancet 2004 — Appropriate body-mass index for Asian populations · WHO — Obesity and overweight fact sheet(WHO technical report series / current global reference)

Morbid obesity, severe obesity, class 3 — the same thing

"Morbid obesity" was the standard clinical term for a BMI of 40.0 or above, or 35.0 and above together with an obesity-related condition such as type 2 diabetes, hypertension or obstructive sleep apnoea. It has largely been replaced by class 3 obesity, which is what the CDC's current adult BMI categories use, and by severe obesity in much of the US clinical literature.

The definition did not change when the name did. The reason for the rename is that "morbid" attaches a prognosis to a person rather than describing a measurement. If you see all three terms in the same document, they are pointing at the same band.

Every standard's obesity ladder, side by side

Not every authority subdivides obesity — and that is the part most comparison tables miss. Korea and Japan publish a full three-class ladder; China, Singapore and the ADA publish a single obesity line; Hong Kong stops at two classes. Each row below is read from the issuing authority's own document.

Obesity classes and their BMI boundaries by issuing authority
Standard	Obesity from	Sub-divisions published
WHO international (global)World Health Organization	≥ 30.0	30 – 35 — Obese class I 35 – 40 — Obese class II ≥ 40 — Obese class III (severe obesity)
WHO Expert Consultation 2004 (Asian populations)World Health Organization expert consultation, published in The Lancet	≥ 27.5	27.5 – 32.5 — High risk ≥ 32.5 — Very high risk
WHO Asia-Pacific (WPRO / IASO / IOTF)WHO Western Pacific Regional Office, International Association for the Study of Obesity, International Obesity Task Force	≥ 25.0	25 – 30 — Obese I ≥ 30 — Obese II
ChinaNational Health Commission of the PRC — health industry standard WS/T 428	≥ 28.0	None. A single obesity band from 28.0 — Obese.
Hong Kong, ChinaDepartment of Health, Centre for Health Protection — adopting the WHO Western Pacific Regional Office classification for Asian adults	≥ 25.0	25 – 30 — Obese I ≥ 30 — Obese II
SingaporeHealth Promotion Board (HPB), Ministry of Health	≥ 27.5	None. A single obesity band from 27.5 — High risk.
JapanJapan Society for the Study of Obesity (JASSO)	≥ 25.0	25 – 30 — Obesity class 1 30 – 35 — Obesity class 2 ≥ 35 — Obesity class 3–4 (high-degree obesity)
South KoreaKorean Society for the Study of Obesity (KSSO)	≥ 25.0	25 – 30 — Obesity class I 30 – 35 — Obesity class II ≥ 35 — Obesity class III
India and South AsiaConsensus statement for Asian Indians (Misra et al., JAPI 2009); Indian Council of Medical Research	≥ 25.0	None. A single obesity band from 25.0 — Obese.
UK NICE guidance — Asian, Chinese, Middle Eastern and Black African/Caribbean adultsNational Institute for Health and Care Excellence (UK), guideline NG246	≥ 27.5	None. A single obesity band from 27.5 — Obesity.
ADA 2026 standard for Asian populationsAmerican Diabetes Association — Standards of Care in Diabetes 2026, adult overweight and obesity	≥ 27.5	None. A single obesity band from 27.5 — Obesity.

The WHO 2004 row is the one exception to how this table reads: 27.5 and 32.5 are public-health action points along the BMI continuum, not clinical obesity classes. The 2004 consultation explicitly kept 25 and 30 as the international definitions rather than redefining them.

Why the classes move five points in Asia

The arithmetic is simple, the consequence is not. Take a BMI of 27.5: on the WHO international ladder it is overweight, a full 2.5 points short of class 1 obesity. On the WHO Asia-Pacific ladder — and under Hong Kong's Department of Health classification and Korea's KSSO guidelines — 27.5 is obese class I. Same body, same number, a different class, from a different continent's guidance.

The reason is the one behind every lower threshold on this site: at the same BMI, people of Asian descent tend to carry more body fat and more visceral fat, so obesity-related disease appears earlier. Korea's 2022 guideline states the position plainly — obesity-related disease risk rises linearly below BMI 25 in Korean adults, which is why the cut-point sits at 25 rather than 30.

Note also that not every Asian standard subdivides. China's WS/T 428 sets obesity at 28.0 and stops there, Singapore's HPB frames everything as risk rather than weight status, and the ADA's 2026 criteria for Asian populations draw a single obesity line at 27.5. Assuming a three-class ladder exists everywhere is the most common error in this area.

Japan draws the line differently again — obesity is not obesity disease

Japan has a class structure that matches Korea's boundaries but names them differently, and then adds a distinction no other standard on this site makes. Under JASSO, obesity is a BMI of 25.0 or more, split into Obesity class 1 (25 – 30), Obesity class 2 (30 – 35), Obesity class 3–4 (high-degree obesity) (≥ 35). But obesity disease (肥満症) is a separate diagnosis: it requires that BMI plus an obesity-related health disorder, or a visceral fat area of 100 cm² or more measured on abdominal CT.

The practical effect is that in Japan a BMI of 32 can be "obesity" without being "obesity disease", and a BMI of 26 can be obesity disease if it comes with a related condition. Being in a class is not the same as having a disease — and that principle generalises, which is why a class label from any of the tables above should be treated as a screening result rather than a diagnosis.

BMI range	Classification
< 18.5	Underweight
18.5 – < 25	Normal weight
25 – < 30	Obesity class 1
30 – < 35	Obesity class 2
≥ 35	Obesity class 3–4 (high-degree obesity)

Source: JASSO — 肥満度分類 (obesity classification table) · Definition, criteria, and core concepts of guidelines for the management of obesity disease in Japan (Endocrine Journal, 2024) · OECD Reviews of Public Health: Japan — on the JASSO BMI 25 threshold(Clinical Practice Guidelines for the Management of Obesity Disease (2022) and JASSO classification)

What actually changes between the classes

Not the label — the escalation. Three concrete rules from the guidelines on this page:

Central obesity can promote you a class. Under the ADA's 2026 standards, inside BMI 23.0–27.4 a waist of 90 cm or more (men) or 80 cm or more (women), or a waist-to-height ratio of 0.5 or more, reclassifies the person as obese rather than overweight. The waist measurement, not the scale, decides which ladder you are on.
Above BMI 35 the waist stops adding information. NICE advises that at this level a waist measurement adds almost no further predictive power — which is the point where the BMI class is the better guide rather than the worse one.
Trajectory matters as much as the class. The ADA's 2026 standards flag a sustained gain of 1–1.5 kg per year over three years as a materially raised risk regardless of your current class. A steady climb through class 1 is a different situation from arriving there and staying.

And the whole set of ladders drawn to one scale, so you can see the disagreement rather than take my word for it:

All eleven standards, side by side

BMI overweight and obesity cut-points by country and authority
Standard	Normal range	Overweight from	Obesity from	Waist / central obesity	Source
WHO international (global)World Health Organization	18.5 – 24.9	25.0	30.0	—	Primary source
WHO Expert Consultation 2004 (Asian populations)World Health Organization expert consultation, published in The Lancet	18.5 – 22.9	23.0	27.5	—	Primary source
WHO Asia-Pacific (WPRO / IASO / IOTF)WHO Western Pacific Regional Office, International Association for the Study of Obesity, International Obesity Task Force	18.5 – 22.9	23.0	25.0	—	Primary source
ChinaNational Health Commission of the PRC — health industry standard WS/T 428	18.5 – 23.9	24.0	28.0	M ≥90cm / W ≥85cm	Primary source
Hong Kong, ChinaDepartment of Health, Centre for Health Protection — adopting the WHO Western Pacific Regional Office classification for Asian adults	18.5 – < 23.0	23.0	25.0	WHtR < 0.5	Primary source
SingaporeHealth Promotion Board (HPB), Ministry of Health	18.5 – 22.9	23.0	27.5	M ≥90cm / W ≥80cm	Primary source
JapanJapan Society for the Study of Obesity (JASSO)	18.5 – 24.9	—	25.0	M ≥85cm / W ≥90cm	Primary source
South KoreaKorean Society for the Study of Obesity (KSSO)	18.5 – 22.9	23.0	25.0	M ≥90cm / W ≥85cm	Primary source
India and South AsiaConsensus statement for Asian Indians (Misra et al., JAPI 2009); Indian Council of Medical Research	18.0 – 22.9	23.0	25.0	M ≥90cm / W ≥80cm	Primary source
UK NICE guidance — Asian, Chinese, Middle Eastern and Black African/Caribbean adultsNational Institute for Health and Care Excellence (UK), guideline NG246	18.5 – 22.9	23.0	27.5	WHtR < 0.5	Primary source
ADA 2026 standard for Asian populationsAmerican Diabetes Association — Standards of Care in Diabetes 2026, adult overweight and obesity	18.5 – 22.9	23.0	27.5	M ≥90cm / W ≥80cm	Primary source

All 11 standards shown, each read from the issuing authority's own document (linked per row). The WHO 2004 figures of 23.0 / 27.5 are public-health action points, not a redefinition of the international categories.

Frequently asked questions

What are the obesity classes?: The WHO divides obesity into three classes by BMI. On the WHO international scale, class 1 is 30.0–34.9, class 2 is 35.0–39.9 and class 3 is 40.0 and above. Class 3 is what older writing called morbid obesity. Where a national standard adopts the Asian obesity line of 25.0 instead of 30.0, all three boundaries shift down by five points.
What BMI is class 3 obesity?: 40.0 or above on the WHO international scale, where obesity itself begins at 30.0. Where the obesity line is 25.0 — Korea's KSSO guidelines and Japan's JASSO classification — class III begins at 35.0 instead. The class structure is identical; the whole ladder has simply moved.
Is "morbid obesity" still used?: It has largely been replaced by "class 3 obesity" in clinical writing, because the older term was felt to be stigmatising. The definition did not change: a BMI of 40.0 or above, or 35.0 or above together with an obesity-related condition such as type 2 diabetes, hypertension or obstructive sleep apnoea.
Do obesity classes change for Asian populations?: The boundaries do, and not every Asian standard subdivides obesity at all. Korea's KSSO runs class I 25.0–29.9, class II 30.0–34.9 and class III 35.0 or above; Japan's JASSO uses the same 25 / 30 / 35 boundaries across four classes, merging 3 and 4 into high-degree obesity. By contrast China's WS/T 428 defines obesity from 28.0 without subdividing it, Hong Kong's Department of Health stops at obese I and II, and the ADA's 2026 Asian criteria set a single obesity line at 27.5.

Data sources and how we verify them

Every cut-point, band and formula on this page is taken from the issuing authority's own document, listed below. We do not use second-hand summaries, and we do not fill gaps with numbers no source states.

World Health Organization (WHO)
International cut-points (25 / 30) and the 2004 Asian action points
National Health Commission of the PRC
China's current adult cut-points — WS/T 428 (24 / 28) and waist criteria
Department of Health, Hong Kong, China
Hong Kong classification (23 / 25), from the Population Health Survey 2020-22
Health Promotion Board, Singapore
Singapore's three-band risk ladder (18.5–22.9 / 23.0–27.4 / ≥27.5)
Japan Society for the Study of Obesity (JASSO)
Japan's classification, which has no overweight tier (obesity from 25)
Korean Society for the Study of Obesity (KSSO)
Korea's classification and abdominal-obesity waist thresholds
Indian Council of Medical Research / Misra consensus
South Asian cut-points, including the 18.0 lower bound
National Institute for Health and Care Excellence (NICE), UK
Lower ethnic-specific thresholds for Asian adults in the UK (23 / 27.5)
American Diabetes Association (ADA)
2026 standards — Asian obesity at 27.5 and central obesity overriding BMI

Cut-points are population-level statistical thresholds, not individual diagnoses. If your value sits near a category line, measure your waist as well and read it alongside body-fat percentage. Last checked: 2026-09-15.

Sources

Every figure above was checked against the original document. This page is general information, not medical advice.

BMI chart by height BMI formula Asian BMI chart by country Waist-to-height ratio BMI calculator for women BMI calculator for men

Other countries and regions

China Hong Kong, China Singapore Japan South Korea India and South Asia Asian BMI chart Waist-to-height ratio

Health Information Disclaimer

Content on this site is for general information only and does not constitute medical advice. Consult a doctor or qualified health professional for personal health concerns. Last updated: August 9, 2026.

We do not keep your information. Height, weight, waist and age are calculated entirely in your browser — nothing is uploaded to our servers, logged or stored, and the numbers are gone as soon as you close or refresh the page. We measure anonymous traffic only, never the values you type. Full detail in our Privacy Policy.