Waist-to-Height Ratio Calculator

About this calculator

Your waist-to-height ratio is your waist circumference divided by your height, with both measured in the same unit — an 80 cm waist at a height of 170 cm is 80 ÷ 170 = 0.47. Because the unit cancels, the answer is identical in centimetres or in inches, which is why this calculator can take a waist in inches against a height in feet and inches and still be right. The ratio is the measure NICE guideline NG246 uses to assess central adiposity — fat carried around the middle — and its headline advice is simply to keep your waist to less than half your height, a ratio under 0.50. Enter your waist and your height to see your ratio, the NICE band it falls in, and the waist measurement that is half your height — the line the guideline asks you to stay under.

How to read your results

The headline figure is your ratio, and the coloured pill beneath it names the NICE band it falls in: 0.40 up to (but not including) 0.50 is healthy central adiposity (no increased health risks), 0.50 up to 0.60 is increased central adiposity (increased health risks), and 0.60 or more is high central adiposity (further increased health risks). A ratio below 0.40 sits under the bottom of NICE's scale, so it is reported as outside the classified range rather than given a label the guideline never defined. The band is decided on your real ratio, so the figure is normally shown to two decimal places and switches to three whenever two would round it across the boundary it sits under: an 84.9 cm waist at 170 cm is shown as 0.499 and banded healthy, because it genuinely is less than half that height. The "half your height" panel is the number you can act on: it works backwards from your height to the waist that is exactly half of it, and tells you how far your current waist is from that line. Landing on the line is a ratio of 0.50, which NICE already counts as increased, so the aim is to be under it rather than on it. If you enter a weight, the calculator also checks your BMI against 35 kg/m² — the ceiling NICE puts on these bands — and says so plainly when you are above it. The result is guidance, not a diagnosis, and it is not meaningful during pregnancy. Read the band you landed in as a description of where your weight sits, not as a verdict on your health. A healthy reading means your waist is less than half your height, which is the position NICE asks people to hold — re-measure every few months rather than chasing a lower number, because there is no benefit band below 0.40. An increased reading means your waist is half your height or more but under 60% of it; NICE associates that with increased risk of type 2 diabetes, high blood pressure and cardiovascular disease, and the change it points to is getting the waist back under half the height. A high reading, 0.60 or more, is the one worth taking to a healthcare professional, who will read it alongside your blood pressure, blood sugar, cholesterol and family history rather than on its own — plenty of people in the upper bands have entirely normal results on all four. A reading under 0.40 is not a better-than-healthy result: NICE classifies nothing there, so treat it first as a prompt to check the tape was at the right landmark, and second — if the measurement is genuinely right — as something to mention alongside a low body weight. In every band the ratio is a screening signal about one thing, fat carried around the middle, and it says nothing about the rest of your health.

How it's calculated

The ratio is waist circumference divided by height, both converted to centimetres first: WHtR = waist ÷ height. The band is decided on that quotient itself, not on a rounded copy of it, because NICE states the same rule twice — recommendation 1.9.14 as bands, and recommendation 1.9.15 as "keep your waist to less than half their height" — and the second is a claim about the real number: an 84.9 cm waist at a height of 170 cm genuinely is less than half that height. The bands are therefore applied as 0.40 up to 0.50 healthy central adiposity, 0.50 up to 0.60 increased central adiposity, and 0.60 or more high central adiposity, with nothing classified below 0.40. Display precision then follows the band rather than the other way round: the ratio is printed to two decimal places, and to three whenever two would round it up across the boundary it sits below, so 84.9 ÷ 170 prints as 0.499 beside "healthy" instead of printing 0.50 beside it. Comparisons allow one part in a billion of slack — under two nanometres of tape at a height of 170 cm — so that a waist entered in inches against a height in feet and inches lands on 0.50 rather than on 0.4999999999. The half-height figure is the same equation inverted, waist = height × ratio, evaluated at 0.40, 0.50 and 0.60. An optional weight produces BMI = weight(kg) ÷ height(m)², used for one purpose only: NICE states its bands for adults with a BMI under 35 kg/m² (recommendation 1.9.8), so a BMI of 35 or more raises a callout saying the guideline does not apply the bands at that point — and that BMI is printed under the same rule, to two decimal places rather than one whenever one would round it up to "35.0". Waist measurements are assumed to follow the WHO expert consultation protocol, which is worth setting out in full because measuring in the wrong place is the single biggest source of a wrong ratio — a tape at the navel, at the trouser waistband, or over a jumper can shift the reading by several centimetres, which is enough to move you a whole band. Step one: find the two landmarks, the lower margin of the least palpable rib and the top of the iliac crest (the top of the hip bone), in the mid-axillary line — the line running down from your armpit. Step two: wrap the tape around the midpoint between them, level and parallel to the floor; NICE phrases the same site in plainer words as "midway between these points (this will be just above the belly button)". Step three: stand upright, feet close together, arms relaxed at your sides, body weight evenly distributed, wearing little clothing — never over a jumper or a coat. Step four: take the reading at the end of a normal expiration; do not breathe in and hold it, do not suck in, and do not pull the tape tight — snug but not constricting, and level all the way round. Step five: measure twice, and if the two readings are within 1 cm of each other average them; if they differ by more than 1 cm, take both again. Other protocols exist and are not interchangeable: the NIH and NHANES III protocols measure at the top of the iliac crest rather than at the midpoint, which generally gives a slightly larger waist. The WHO consultation's review of 120 studies found the choice of protocol had no substantial influence on the association between waist circumference and health outcomes — but for one person's number, the site you use still moves the reading, so measure the same way every time you re-check it.

Worked example

A person measures a waist of 96.5 cm and stands 170 cm tall. This is the metric worked example NICE prints in NG246.

96.5 ÷ 170 = 0.5676, shown as 0.57 — increased central adiposity, which NICE associates with increased health risks. Half of this height is 170 × 0.50 = 85.0 cm, so the waist is 11.5 cm above the line NICE asks people to stay under; it is getting below 85.0 cm, not down to it, that reaches the healthy band, because a waist of exactly half your height is a ratio of 0.50 and NICE bands 0.50 as increased. The same person measured in inches — 38 in and 67 in — gives 38 ÷ 67 = 0.5672, also 0.57, because the ratio is dimensionless.

Frequently asked questions

What is a healthy waist-to-height ratio?

NICE guideline NG246 (recommendation 1.9.14) classifies a waist-to-height ratio of 0.4 to 0.49 as healthy central adiposity, indicating no increased health risks. From 0.5 to 0.59 is increased central adiposity, indicating increased health risks, and 0.6 or more is high central adiposity, indicating further increased health risks. The guideline puts the same idea in one sentence for patients (recommendation 1.9.15): keep your waist to less than half your height — so the healthy band runs from 0.40 up to, but not including, 0.50, and a ratio of exactly 0.50 is already the increased band. NICE states these bands for adults with a BMI under 35 kg/m² (recommendation 1.9.8), of both sexes and all ethnicities, including adults with high muscle mass.

What waist size should I have for my height?

Multiply your height by 0.5 — that is the waist that puts you exactly on the boundary NICE asks people to stay under. At 170 cm the answer is 85.0 cm; at 5 ft 7 in (67 in) it is 33.5 in; at 180 cm it is 90.0 cm. Anything under that figure keeps you in the healthy band as long as you are also at or above 0.40; landing exactly on it is a ratio of 0.50, which NICE bands as increased rather than healthy. Multiplying your height by 0.6 gives the waist at which NICE's high central-adiposity band begins — 102.0 cm at a height of 170 cm.

How do I measure my waist correctly?

The WHO expert consultation on waist circumference specifies the midpoint between the lower margin of the least palpable rib and the top of the iliac crest, in the mid-axillary line, with the tape parallel to the floor. Stand upright with your feet close together, arms at your sides and your weight evenly distributed, wearing little clothing, and take the reading at the end of a normal expiration — not holding a breath in, and not sucking in. Measure twice: if the two readings are within 1 cm of each other, average them; if they differ by more, take both again. Measuring at the navel, at your trouser waistband, or over a jumper can move the reading by several centimetres, which is enough to move you a whole band.

Is waist-to-height ratio better than BMI?

They answer different questions. BMI compares your weight with your height and cannot tell muscle from fat; waist-to-height ratio measures where the weight sits, which is what makes it a practical estimate of central adiposity. NICE recommends using waist-to-height ratio alongside BMI for adults with a BMI under 35 kg/m² (recommendation 1.9.8), explicitly including adults with high muscle mass, whose BMI can read high while their ratio does not. Above a BMI of 35 kg/m² NICE uses BMI instead and does not recommend measuring waist circumference for this purpose.

Does the ratio work in inches as well as centimetres?

Yes, provided both measurements use the same unit. The ratio is dimensionless — the unit cancels in the division — so 38 in ÷ 67 in and 96.5 cm ÷ 170 cm both give 0.57, which is exactly why NICE prints the same worked example twice. What you must never do is divide across units: a 35.4 in waist against a 170 cm height gives 0.21, a number with no meaning. This calculator converts everything to centimetres internally, so mixing an inch waist with a feet-and-inches height is safe here even though it is not safe on paper.

When does waist-to-height ratio not apply?

The ratio is not meaningful during pregnancy, when waist circumference reflects the pregnancy rather than central adiposity. NICE also scopes its bands to adults with a BMI under 35 kg/m² (recommendation 1.9.8): above that, the guideline assesses weight-related risk with BMI and does not recommend measuring waist circumference for this purpose. Below 0.40 the guideline classifies nothing at all, so a very low ratio is reported here as outside the classified range — worth re-checking the measurement site, and worth raising with a healthcare professional if it is genuine. In every case the ratio is a screening signal, not a diagnosis.

Sources

• www.nice.org.uk/guidance/ng246/chapter/Identifying-and-assessing-overweight-obesity-and-central-adiposity — National Institute for Health and Care Excellence
• www.who.int/publications/i/item/9789241501491 — World Health Organization
• iris.who.int/handle/10665/44583 — World Health Organization

Reviewed by the YouCalc Team · Last reviewed May 24, 2026