Waist-to-height ratio: the half-your-height rule, how to measure your waist, and what the bands mean

How to work out waist-to-height ratio

Divide your waist circumference by your height, with both in the same unit: centimetres over centimetres or inches over inches. The answer has no unit, so 0.48 means the same thing whether you measured in metric or imperial. NICE's guideline says it directly: measure waist circumference and height "in the same units (either both in centimetres, or both in inches)" (NICE NG246, Box 1).

The rule that comes with it is the simplest health message in the guideline: keep your waist to less than half your height. A ratio of exactly 0.5 is the boundary, so the quickest check needs no division at all. Halve your height and compare.

Work to two decimal places. NG246 writes its bands as 0.4 to 0.49 and 0.5 to 0.59, so a ratio that rounds to 0.50 is on the boundary, and the plain-language rule, under half your height, is the tie-break.

The NICE bands and who they apply to

NICE classifies waist-to-height ratio in three bands: 0.4 to 0.49 is healthy, 0.5 to 0.59 is increased central adiposity and 0.6 or more is high central adiposity. These are recommendations 1.9.14 for adults and 1.10.10 for children and young people in NICE guideline NG246, Overweight and obesity management, published on 14 January 2025 and last updated on 8 January 2026.

The health risks NG246 names are type 2 diabetes, hypertension and cardiovascular disease. The bands measure central adiposity, fat carried around the middle, which is the thing BMI cannot see.

Who the bands are for matters as much as the numbers:

• Adults with a BMI below 35 kg/m². Recommendation 1.9.8 says to measure and use waist-to-height ratio "as well as" BMI in this group. At 35 or more, NICE uses BMI alone. The US National Heart, Lung, and Blood Institute's 2000 practical guide gives the reason for waist measures generally: at a BMI of 35 or more, waist circumference "adds little to the predictive power" of the BMI classification.
• Both sexes and all ethnicities, including adults with high muscle mass. The same three bands apply to everyone, unlike BMI, where NICE lowers the thresholds for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background (recommendation 1.9.11; the BMI calculator shows the WHO's equivalent action points).
• Children and young people aged 5 and over. NICE's January 2026 update amended recommendations 1.10.5, 1.10.10 and 1.10.11 "to clarify that waist-to-height ratios should only be used" in this age group. Under 5, there is no waist-to-height classification.

NG246 gives no band below 0.4. A low ratio is outside what the guideline classifies, and a very low one is a question for a clinician, not a better score.

2022 or 2025? Why the dates disagree

Pages that rank for this question give both years, and both are right about different documents. NICE first added waist-to-height ratio in an update to its older obesity guideline, CG189, in 2022, which is the date most newspaper copies carry. NG246, published in January 2025, replaced CG189 and six other NICE obesity guidelines and kept the same bands, now numbered 1.9.14 and 1.10.10. The current text is NG246's.

How to measure your waist: three bodies, two landmarks

NICE measures the waist midway between the bottom of the ribs and the top of the hips, usually just above the belly button, after breathing out naturally. That is Box 1 of NG246: find the bottom of the ribs and the top of the hips, wrap the tape "midway between these points", and breathe out naturally before taking the measurement.

The World Health Organization's STEPS surveillance manual (Part 3, Section 5, last updated 26 January 2017) uses the same midpoint, between "the lower margin of the last palpable rib and the top of the iliac crest (hip bone)". The US NHLBI's 2000 practical guide uses a different point: the tape goes around the abdomen "at the level of the iliac crest", the top of the hip bone itself.

Does the landmark change the number?

Yes, especially in women. Wang and colleagues measured 111 adults at four sites in 2003: just below the lowest rib, the narrowest point, the midpoint between rib and iliac crest, and just above the iliac crest. In women every site differed: the narrowest point gave the smallest figure, then the lowest rib, then the midpoint, and just above the iliac crest the largest. In men the narrowest point was the smallest of the four (Am J Clin Nutr 77(2):379-384). Every site was highly repeatable, so the difference is the landmark, not the tape.

Whether the site changes the link with disease is a separate question. A 2008 review of 120 studies by Ross and colleagues found that the measuring protocol had "no substantial influence" on the association between waist circumference and death, heart disease or diabetes (Obesity Reviews 9(4):312-325). The practical rule follows from both: if you compare your ratio with NICE's bands, use NICE's midpoint, and use the same point every time you measure.

A measuring routine that gives the same answer twice

1. Stand with your feet together and your weight even, arms relaxed at your sides, on bare skin or over thin clothing.
2. Find the bottom of your lowest rib and the top of your hip bone on one side, and mark the midpoint with a finger or a washable pen.
3. Wrap the tape level all round, at that height on both sides. A mirror shows whether it dips at the back.
4. Breathe normally for a few breaths, breathe out, and read the tape without pulling it into the skin.
5. Measure height without shoes or headwear, looking straight ahead; the WHO manual reads it to the nearest millimetre.
6. Write both numbers in the same unit, then divide.

The string test

A string cut to your height and folded in half is the whole test. Wrap it round your waist at the measuring point: if the ends meet, your waist is under half your height. Margaret Ashwell, who first proposed the 0.5 boundary, describes the "Ashwell String Test" in her 2025 account in Nutrition Today as the reason "you didn't even need a tape measure". It answers one question, above or below 0.5, and nothing finer.

Worked examples in centimetres and inches

Each example divides waist by height in one unit and reads the band off NICE's table.

Example A: metric, healthy band

Height 170 cm, waist 82 cm, BMI 24. 82 ÷ 170 = 0.482, so 0.48: healthy central adiposity. The quick check agrees: half of 170 is 85, and 82 is under it.

Example B: imperial, just over half

Height 5 ft 9 in, which is 69 inches; waist 36 inches. 36 ÷ 69 = 0.522, so 0.52: increased central adiposity. Half of 69 is 34.5 inches, so this waist is 1.5 inches over the line. The same man is well under NHLBI's waist threshold for men, 40 inches (102 cm), which shows why a height-scaled measure flags risk that a fixed waist cut-off can miss.

Example C: a fixed cut-off misses a shorter man

Height 165 cm, waist 100 cm. 100 ÷ 165 = 0.606, so 0.61: high central adiposity. NHLBI's men's threshold is a waist over 102 cm, which this man does not reach. At 190 cm tall, the same 100 cm waist would give 0.53, increased but not high. A fixed waist cut-off treats both men alike; the ratio does not.

Example D: the unit mistake

Waist 34 inches, height 170 cm. 34 ÷ 170 = 0.20, a ratio no adult has. Convert first: 34 inches is 86.4 cm, and 86.4 ÷ 170 = 0.51. Any result below about 0.35 for an adult is worth checking for mixed units before anything else.

Waist-to-height ratio, BMI and waist circumference compared

Waist-to-height ratio adds where fat sits to what BMI tells you, and it scales with height where a fixed waist cut-off does not. A 2012 systematic review and meta-analysis by Ashwell, Gunn and Gibson, of 31 studies with more than 300,000 adults, found that compared with BMI, waist circumference improved the discrimination of cardiometabolic outcomes by 3% and waist-to-height ratio by 4 to 5% (Obesity Reviews 13(3):275-286).

The UK data behind NICE's change make the point with numbers. Gibson and Ashwell analysed 4,112 adults in the Health Survey for England and found that nearly one-third of the people the older BMI and waist "matrix" placed at no increased risk had a waist-to-height ratio of 0.5 or more (British Journal of Nutrition 123(6):681-690). Among the people the matrix called no increased risk, 23% had hypertension; among those with a ratio under 0.5, 9% did.

Waist-to-height ratio is also one of the three body measures named by the 2025 Lancet Commission on clinical obesity, which says excess fat should be confirmed by direct measurement or by BMI plus at least one of waist circumference, waist-to-hip ratio or waist-to-height ratio, with "age- gender- and ethnicity-appropriate cut-off points" (Rubino et al., Lancet Diabetes & Endocrinology 13(3):221-262). The Commission does not set its own number; NICE's 0.5 is one of the cut-offs a clinician would use in the UK.

The sex-specific charts on calculator sites

Many calculator pages show separate bands for men and women, with men "healthy" up to 0.52; NICE uses one set of bands for both sexes, and 0.52 is in its increased-risk band. The charts usually run from "extremely slim" at 0.34 or below through "healthy", "overweight" and "obese", with women's healthy range around 0.42 to 0.48 and men's around 0.43 to 0.52. None of the pages we checked names where those numbers come from.

The primary sources do not support them. NG246 says its classifications "can be used for people with a BMI under 35 kg/m² for both sexes and all ethnicities, including adults with high muscle mass", and the same three bands appear in its children's recommendation. A man at 0.51 reading one of these charts is told he is healthy; under NICE he is in the increased-risk band and is advised to bring his waist under half his height.

There is real scientific debate about the 0.5 boundary, but it runs on height, not sex. Nevill and colleagues, using three samples totalling 58,742 people, found that a fixed ratio over-classifies shorter adults as at risk, and proposed dividing the waist by the square root of height instead (Obesity Research & Clinical Practice 17(1):1-8). That index has not been adopted by NICE, which kept the simple ratio when it updated NG246 in 2026.

Where 0.5 and 0.6 come from

The 0.5 boundary is where heart-disease risk was seen to start in UK survey data in the 1990s; the 0.6 boundary was set so the top band held about as many people as a BMI over 30. Margaret Ashwell describes both choices in her 2025 Nutrition Today account. Her Health Survey for England research found coronary heart disease risk starting at a ratio of about 0.5, supported by a Japanese group that had proposed the ratio shortly before, and she drew the first Ashwell Shape Chart with that boundary in 1996.

The upper boundary was, in her words, determined "on the basis of common sense": the 0.6 band was set to contain roughly the same proportion of the population as the top BMI category. The 0.4 floor of the healthy band completes the chart. Ashwell sat on the NICE committee that wrote NG246, and she notes that NICE's own evidence review did not use her cross-sectional studies, which is worth knowing: the bands NICE adopted rest on its own analysis, which included 76 prospective studies in adults and 42 in children.

What this guide does not cover

This guide explains how waist-to-height ratio is calculated and how NICE classifies it. It is educational, not medical advice: a ratio is a screening number, and what it means for you, alongside blood pressure, blood tests and history, is for your doctor or nurse to judge. NG246 itself frames it that way, telling adults with a ratio in the increased bands to seek clinical advice.

It does not cover pregnancy, for which NG246 gives no waist-to-height guidance, children under 5, or people with a BMI of 35 or more. It also does not cover body-fat percentage, waist-to-hip ratio or the US military's body composition rules. Simple Online Counter is a free, browser-based set of counters and calculators; its BMI calculator works out the other half of NICE's assessment and keeps your entries in your own browser.