BMI Calculator for Japan
Japan has no "overweight" — 25 is obesity
Under Japan Society for the Study of Obesity (JASSO)'s scale, Japan uses a normal range of BMI 18.5 – 24.9, overweight from — there is no separate overweight band, obesity is defined directly from 25.0.
Asian BMI Calculator
Measure at the midpoint between your lowest rib and the top of your hip bone, on a normal breath out. Needed to assess central obesity and waist-to-height ratio.
This calculator covers 11 published standards: WHO international, the WHO 2004 Asian action points, WHO Asia-Pacific, China's WS/T 428, Hong Kong Department of Health, Singapore HPB, Japan JASSO, Korea KSSO, the Misra Indian consensus and ADA 2026. BMI is a screening tool, not a diagnosis.
Japan BMI classification
| 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)
Why Japan's cut-points look the way they do
Japan is the outlier that breaks most comparison tables. JASSO defines obesity as a BMI of 25 or more and has no intermediate overweight category at all: the normal band runs from 18.5 up to just under 25, and everything above is obesity, subdivided into four classes.
This is a different structure from China (24/28), Korea (23/25) or the WHO Asia-Pacific scale (23/25). Japan did not lower the obesity line — it moved the overweight line up to meet it and deleted the tier.
The reason is stated in JASSO's own guidelines: Japanese people develop obesity-related disorders such as glucose intolerance, dyslipidaemia and hypertension at lower BMI than people of European descent, so 25 was chosen as the point at which the mean number of obesity-related disorders exceeds one.
JASSO also splits obesity from obesity disease (肥満症). Obesity is a BMI of 25 or more; obesity disease requires that BMI plus a related health disorder, or a visceral fat area of 100 cm² or more on CT. Japan treats the second as a disease entity requiring treatment — the first is not automatically one.
Key points
- No overweight band. Normal runs 18.5–<25 and obesity begins immediately at 25.
- Four obesity classes, with class 3–4 (≥35) treated as high-degree obesity requiring a different treatment strategy.
- Visceral fat area ≥100 cm² on CT is the primary visceral-obesity criterion — waist is only a screening trigger.
- Waist screening thresholds are unusual: ≥85 cm for men but ≥90 cm for women.
How Japan compares
| Compared with | Overweight threshold | Obesity threshold |
|---|---|---|
| WHO international (global) 25 / 30 | no separate overweight band | 5.0 points lower |
| WHO Asia-Pacific (WPRO / IASO / IOTF) 23 / 25 | no separate overweight band | same |
A BMI of 25.0 is classified as Obesity class 1 in Japan (Obesity class 1). The same value reads differently on the WHO international scale — which is why the scale has to be named.
Waist circumference and central obesity
JASSO's primary criterion is not waist circumference but visceral fat area of 100 cm² or more on abdominal CT. Waist is used only as a screening trigger to decide who gets the scan — and the screening thresholds are ≥85 cm in men and ≥90 cm in women.
Waist matters because BMI cannot see where fat sits. Two people with the same BMI can have very different visceral fat, and visceral fat is the component most strongly linked to type 2 diabetes and cardiovascular disease. The ethnicity-independent screen is waist-to-height ratio: keep your waist below half your height.
All standards side by side
| 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
- Why does Japan have no overweight category?
- Because JASSO's threshold of 25 was derived as the point where the average number of obesity-related health disorders exceeds one in Japanese health-checkup cohorts. The 25 line is already the action threshold, so there is no room for a separate overweight tier below it.
- Is Japanese BMI 25 obese?
- Yes under the JASSO classification. But it is not automatically "obesity disease" (肥満症) — that requires an accompanying obesity-related disorder or a visceral fat area of 100 cm² or more. The distinction decides whether treatment is indicated.
- Why is the waist screening threshold higher for Japanese women than men?
- JASSO uses ≥85 cm for men and ≥90 cm for women purely as a screening trigger for abdominal CT, because Japanese women accumulate visceral fat at a larger waist circumference than men. It is not a diagnosis threshold — the CT reading is.
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
- 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
Every figure above was checked against the original document. This page is general information, not medical advice.
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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.
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Standard documented on this page: Japan Society for the Study of Obesity (JASSO) — Clinical Practice Guidelines for the Management of Obesity Disease (2022) and JASSO classification. This site documents 11 published standards; figures are read from each authority's own document.