Is your waist under half your height?
Slide to your waist and your height and the tool gives the ratio to two decimals, placed on the four bands NICE uses for adults. Add your weight and you also get a BMI figure, with a note on why the ratio is the better screen for central fat.
Two tape measurements, one ratio.
Slide to your waist and your height. The ratio updates as you go and lands on the four bands NICE uses for adults, with the half-your-height line at 0.50.
Your waist is 49 percent of your height: within the healthy band.
- May be lowbelow 0.40
- Healthy0.40 to 0.49
- Increased risk0.50 to 0.59
- High risk0.60 and above
Add your weight above and a BMI figure appears here next to the ratio.
BMI counts every kilogram, muscle and bone included, and cannot tell where the fat sits. The ratio is the better screen because it captures central fat, the kind around the organs that drives cardiometabolic risk.
How to measure
A tape and 1 minute- Find the spotMidway between the lowest rib and the top of the hip bone, which for most adults is just above the navel.
- Breathe out firstMeasure at the end of a normal breath out, without pulling the stomach in or pushing it out.
- Snug, not tightThe tape rests on the skin and stays level all the way round; it should not press into the skin.
- In the morningBefore breakfast, on 2 or 3 days, then take the average. Meals and the time of day can add 1 to 2 cm.
Adults only. The bands are not designed for pregnancy, for under 18s or for a BMI of 35 and above, where NICE says the ratio adds little. A raised figure is a prompt to talk to your GP, not a diagnosis.
How it works.
- Slide to your waist, taped midway between the lowest rib and the hip bone after breathing out, and to your height.
- Read the ratio and where it sits on the four bands: the healthy band runs from 0.4 to 0.49, with the half-your-height line at 0.5.
- Add your weight for a BMI comparison, then save the card or share it.
Where the 0.5 line comes from
NICE brought the waist to height ratio into its obesity guidance in 2022 and kept it in the current guideline, NG246. For adults with a BMI under 35 it asks clinicians to use the ratio alongside BMI, with a message short enough to remember: keep your waist to less than half your height. The bands are 0.4 to 0.49 for healthy central adiposity, 0.5 to 0.59 for increased and 0.6 or more for high. They apply to all ethnic groups and to both sexes, which BMI cut-offs do not: South Asian, Chinese and Black African adults, for example, carry more cardiometabolic risk at a given BMI. In tape terms, a 172 cm adult crosses the half-height line at 86 cm of waist, a 160 cm adult at 80 cm.
Why central fat is the number that matters
Fat around the abdominal organs behaves differently from fat under the skin of the hips and thighs. It releases fatty acids and inflammatory signals straight into the liver, and it tracks closely with insulin resistance, raised triglycerides and higher blood pressure. A 2012 meta-analysis by Ashwell and colleagues, pooling 31 studies with more than 300,000 adults, found the ratio a better predictor of diabetes, hypertension and cardiovascular outcomes than BMI or waist circumference alone. BMI cannot see any of this. It divides weight in kilograms by height in metres squared and sorts everyone into the four WHO classes: under 18.5 underweight, 18.5 to 24.9 normal, 25 to 29.9 overweight, 30 and above obesity. A rugby forward and a sedentary office worker can share a BMI of 28 with very different waists. Muscle is what keeps the ratio down with age, so strength training after 40 and breaking up long stretches of sitting move this number more reliably than the scales do, and both are tied to a longer healthspan.
What this tool is not
It is a screening number, not a diagnosis, and it depends on where the tape sits: a 3 cm difference in circumference moves a 172 cm adult's ratio by about 0.02, enough to cross a band line. The bands are not designed for pregnancy, for anyone under 18, or for a BMI of 35 and above, where NICE says the ratio adds little. Very muscular people can read overweight on BMI and healthy on the ratio; that is the ratio working as intended. If your figure sits at 0.5 or above, the useful next step is a conversation with your GP about blood pressure, blood sugar and lipids, not a crash diet.
Frequently asked.
Where exactly do I put the tape?
Midway between the lowest rib and the top of the hip bone, which for most adults is just above the navel. Breathe out normally, keep the tape level and snug without pressing in, and read it at the end of the breath.
Is 0.5 really the line for everyone?
NICE uses the same half-your-height message for adults of all ethnic groups and both sexes, which is one reason it prefers the ratio to BMI cut-offs. It is not meant for pregnancy, for under 18s or for a BMI of 35 and above.
My BMI is in the normal range but my ratio is 0.53. Which one should I believe?
The ratio. A normal BMI with a waist above half your height is the pattern the guideline was written to catch, because central fat carries the risk that BMI cannot see. Talk it through with your GP rather than dieting hard.
How much can the tape position change the result?
A tape that sits 3 cm higher or lower on the trunk can change the circumference by 2 to 4 cm, which for a 172 cm adult moves the ratio by about 0.02, enough to cross a band line. Measure on 2 or 3 mornings in the same spot and use the average.
Does the ratio work for children?
The tool is for adults. Children's proportions change as they grow and the NICE bands were derived from adult data, so growth charts are the right reference for anyone under 18.
How fast does the ratio change?
Slowly, and that is normal. Roughly 1 cm of waist per kilogram lost is the usual rule of thumb, so 4 kg moves a 172 cm adult's ratio by about 0.02, and the change shows on the tape before it shows on the scales.
Guides behind this tool
Longevity
Healthspan versus lifespan: the years that count
Health
Blood pressure: the two numbers explained
Health
Strength training after 40: how much is enough
Health
Sitting: how much is too muchMore tools
This calculator gives a screening ratio for adults from two tape measurements; it is not a diagnosis, a body composition test or medical advice. The bands are not designed for pregnancy, for under 18s or for a BMI of 35 and above, and a raised figure is a reason to talk to your GP, not to diet on your own. This page is for general information and does not replace medical advice.