What this calculator works out
This calculator divides your waist measurement by your height, both in the same units, and compares the result against the widely used guide of keeping your waist to less than half your height.
It is a simpler measure than BMI and, for many purposes, a more informative one, because where fat is carried matters more to health risk than how much you weigh.
Enter your details
Select Calculate to see where a result falls on this scale.
- Below the usual guide 0.3 to 0.4
- Within the usual guide 0.4 to 0.5
- Above the usual guide 0.5 to 0.6
- Well above the usual guide 0.6 to 0.7
Before you measure
- Measure at the midpoint between the lowest rib and the top of the hip bone, not at the narrowest point and not where your trousers sit.
- Measure directly against the skin or over light clothing, standing upright, after breathing out normally.
- Do not pull the tape tight. It should sit flat without compressing.
- Use the same units for both figures. Centimetres for both, or inches for both — the ratio is the same either way.
Fat stored around the abdomen sits close to the liver, pancreas and other organs and is more strongly associated with type 2 diabetes and cardiovascular disease than fat stored on the hips and thighs. Two people of identical BMI can carry very different amounts of it.
How this calculator works
One division against a single threshold:
Ratio = waist ÷ height
Below 0.4 — below the usual guide
0.4 to 0.5 — within the usual guide
0.5 to 0.6 — above the usual guide
0.6 and above — well above the usual guideThe 0.5 figure is the one to remember: keep your waist to less than half your height. It has the practical advantage of being the same for adults regardless of sex, age or ethnicity, which is not true of BMI thresholds.
NICE guidance recommends this measure alongside BMI for assessing health risks in adults with a BMI under 35.
Worked example: 85 cm waist at 175 cm
Using the default figures — an 85 cm waist and 175 cm height:
- Ratio: 85 ÷ 175 = 0.49
- Within the usual guide, but only just
Half of 175 cm is 87.5 cm, so this measurement sits 2.5 cm inside the guide. That closeness is worth noticing: a small change in either direction moves the result across the threshold, and the practical message is not "you are fine" but "this is the boundary". The same person's BMI of 24.5 gave a similar answer, which is reassuring — the two measures agreeing is more informative than either alone.
Common mistakes
- Measuring at the narrowest point. Use the midpoint between the lowest rib and the hip bone.
- Using your trouser size. Clothing sizes are inconsistent and usually smaller than the true measurement.
- Breathing in or holding the stomach. Breathe out normally and let the tape sit.
- Mixing units. Both figures must use the same unit or the ratio is meaningless.
- Measuring over thick clothing. This can add several centimetres.
Frequently asked questions
Is this better than BMI?
For many purposes, yes. It captures where fat is carried, works with a single threshold across sexes and ethnicities, and handles muscular people better than BMI does. It is not a replacement — NICE guidance recommends using it alongside BMI rather than instead of it, and neither tells you anything on its own about blood pressure, cholesterol or blood glucose.
Does the 0.5 guide apply to children?
It is sometimes applied to children over five, but children are more usually assessed against age and sex percentile charts. If you are concerned about a child's growth or weight, a GP or health visitor is the right place to start rather than a ratio.
Where exactly is the right place to measure?
Find the bottom of your lowest rib and the top of your hip bone on the same side, and measure halfway between them. For most people this is at or slightly above the navel, though it varies. Consistency matters more than precision if you are tracking change — measure the same way each time.
My ratio is above 0.5. What now?
It is a prompt to look at the wider picture rather than a diagnosis. A GP appointment can check blood pressure, cholesterol and blood glucose, which say considerably more about health risk than any measurement you can take at home. Small sustained changes to activity and diet move this ratio more reliably than short-term efforts.
Is my measurement stored?
No. Waist and height are processed in your browser and never transmitted or retained. If thinking about weight, food or body shape is causing you distress, these tools are unlikely to help and may make things harder. Beat, the UK eating disorder charity, runs a free helpline and online support, and a GP can refer you to specialist services.
Related tools
References
- NHS — waist measurement guidance and healthy weight information
- National Institute for Health and Care Excellence — guidance recommending waist-to-height ratio alongside BMI
Sources are checked at publication and can change — how I choose and check references.