Body mass index (BMI) compares weight with height, but it can’t tell where the weight is. Fat stored deep around the belly — doctors call it central adiposity — is the kind most closely tied to health problems. The waist-to-height ratio is a quick way to estimate it at home with nothing more than a tape measure. In England, the National Institute for Health and Care Excellence (NICE) now recommends it alongside BMI for adults.
How to measure your waist
Most mistakes come from measuring in the wrong place. Your waist for this purpose is not where your trousers sit. NICE gives a simple method:
- Find the bottom of your ribs and the top of your hip bones.
- Wrap a tape measure around your middle halfway between them — usually just above the belly button.
- Stand up straight and breathe out normally. Don’t hold your stomach in.
- Measure your height in the same units — both in centimetres, or both in inches.
- Enter both numbers above. The calculator divides waist by height for you.
“Find the bottom of the ribs and the top of the hips. Wrap a tape measure around the waist midway between these points (this will be just above the belly button) and breathe out naturally before taking the measurement. … Measure waist circumference and height in the same units (either both in centimetres, or both in inches). … Divide waist measurement by height measurement.”
Measure on bare skin or thin clothing, and take the reading twice. If the two readings differ, use the average.
A worked example
NICE’s own example: a person who is 170 cm tall with a waist of 96.5 cm has a ratio of 96.5 ÷ 170 = 0.57. That is in the increased central adiposity band (0.50 to 0.59), which NICE says indicates increased health risks.
Measured in inches, the same person comes out at 0.57 — the units cancel out, so the answer doesn’t change. To stay under NICE’s half-height rule, this person’s waist would need to be under 85.0 cm.
A second case shows why the ratio is useful even when BMI looks fine. Someone 165 cm tall who weighs 64 kg has a BMI of 23.5 — “healthy weight”. But with an 88 cm waist their ratio is 0.53, in the increased central adiposity band. Weight that sits around the middle can be missed by BMI alone.
How the bands work
The calculator divides your waist by your height and rounds to two decimal places, the way NICE writes its examples. It then compares the result with NICE’s three published bands:
- 0.40 to 0.49: healthy central adiposity — no increased health risks.
- 0.50 to 0.59: increased central adiposity — increased health risks.
- 0.60 or more: high central adiposity — further increased health risks.
“Classify the degree of central adiposity based on waist-to-height ratio as follows: healthy central adiposity: waist-to-height ratio 0.4 to 0.49, indicating no increased health risks; increased central adiposity: waist-to-height ratio 0.5 to 0.59, indicating increased health risks; high central adiposity: waist-to-height ratio 0.6 or more, indicating further increased health risks.”
NICE also offers a rule of thumb that is easy to remember:
“When talking to a person about their waist-to-height ratio, explain that they should try and keep their waist to less than half their height (so a waist-to-height ratio of under 0.5).”
A ratio below 0.40 is shown but not given a band, because NICE doesn’t define one. If you add your weight, the calculator also works out your BMI and adult category using the same cut-offs as our obesity class calculator.
What the result can’t tell you
A ratio is a screening number. It points to a possible risk; it doesn’t diagnose anything. Keep these limits in mind:
- It is for adults with a BMI under 35. NICE’s bands were set for that group. Above it, BMI alone already places a person in obesity class 2 or 3.
- These bands are for adults. For children and young people aged 5 and over, NICE points families to the NHS children’s waist-to-height calculator instead.
- It doesn’t cover pregnancy. NICE’s guideline leaves pregnancy out, and waist size changes then for other reasons.
- Technique matters. A tape placed a few centimetres too low or too high can move the result by a band.
“These classifications can be used for people with a BMI under 35 kg/m2 of both sexes and all ethnicities, including adults with high muscle mass. The health risks associated with higher levels of central adiposity include type 2 diabetes, hypertension and cardiovascular disease.”
The same caution applies to BMI, which NICE says should be read carefully in very muscular adults and in people aged 65 and over. If your result worries you, a GP or other health professional can check it properly and look at other risk factors such as blood pressure and blood sugar.
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The bigger picture
No large survey on this site records waist size, so we can’t say how many people fall in each band. What the data does show is how obesity measured by BMI, and diabetes — one of the conditions NICE links to central adiposity — have risen together. In 2024, WHO estimates that 16.2% of the world’s adults were living with obesity; in 2022, 14.1% were living with diabetes.
Adult obesity and diabetes worldwide
What this means: Both rates have climbed since 1990. Obesity: 6.7% → 16.2%; diabetes: 6.8% → 14.1%.
- Obesity
- Diabetes
Show the numbers as a table
| Year | Obesity | Diabetes |
|---|---|---|
| 1990 | 6.7% | 6.8% |
| 1991 | 6.8% | 7.0% |
| 1992 | 7.0% | 7.1% |
| 1993 | 7.2% | 7.3% |
| 1994 | 7.4% | 7.4% |
| 1995 | 7.6% | 7.5% |
| 1996 | 7.8% | 7.7% |
| 1997 | 8.0% | 7.8% |
| 1998 | 8.2% | 7.9% |
| 1999 | 8.5% | 8.1% |
| 2000 | 8.7% | 8.2% |
| 2001 | 9.0% | 8.4% |
| 2002 | 9.3% | 8.6% |
| 2003 | 9.5% | 8.7% |
| 2004 | 9.8% | 8.9% |
| 2005 | 10.1% | 9.1% |
| 2006 | 10.4% | 9.3% |
| 2007 | 10.6% | 9.5% |
| 2008 | 10.9% | 9.7% |
| 2009 | 11.2% | 9.9% |
| 2010 | 11.5% | 10.1% |
| 2011 | 11.8% | 10.3% |
| 2012 | 12.1% | 10.6% |
| 2013 | 12.4% | 10.8% |
| 2014 | 12.7% | 11.1% |
| 2015 | 13.0% | 11.4% |
| 2016 | 13.3% | 11.7% |
| 2017 | 13.6% | 12.1% |
| 2018 | 14.0% | 12.4% |
| 2019 | 14.3% | 12.8% |
| 2020 | 14.6% | 13.2% |
| 2021 | 15.0% | 13.7% |
| 2022 | 15.4% | 14.1% |
Adults (18+) with obesity, BMI ≥ 30 (age-standardized); Adults (18+) with diabetes (age-standardized).
Source: WHO Global Health Observatory.
See how your country compares on the world map, or read why it matters. CDC splits adult obesity into class 1 (BMI 30 to under 35), class 2 (35 to under 40) and class 3, also called severe obesity (40 or more).
Sources
- National Institute for Health and Care Excellence (NICE), Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity (published ; checked )
- National Institute for Health and Care Excellence (NICE), Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity (published ; checked )
- National Institute for Health and Care Excellence (NICE), Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity (published ; checked )
- National Institute for Health and Care Excellence (NICE), Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity (published ; checked )
- National Institute for Health and Care Excellence (NICE), Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity (published ; checked )
- US Centers for Disease Control and Prevention, Adult BMI Categories (published ; checked )
- World Health Organization, Global Health Observatory: NCD risk factor estimates
How we process every dataset is explained on How we calculate; all sources are listed on Data sources.
Last updated
Written by the ObesitySurvey team. Not medical advice. Data last rebuilt 1 October 2026.