How to measure and calculate
Stand upright and find the bottom of your ribs and the top of your hips. Place a flexible tape midway between those points, usually just above the belly button. Wrap it level around the body without compressing the skin, breathe out naturally, and read the circumference. Measure standing height and enter both values in centimetres or both in inches.
The formula is waist circumference divided by height. For 80 cm and 160 cm, the ratio is 0.5 and the waist is 50% of height. For 32 inches and 68 inches, the ratio is about 0.47. Units cancel only when both inputs use the same unit. This page uses one unit selector to prevent a silent centimetre–inch mismatch.
How to read the result
The NHS public calculator says to try to keep waist size below half of height and uses the ratio alongside BMI. This page therefore reports whether the exact unrounded value is below 0.5 or is 0.5 and above. It does not add an invented diagnosis, treatment plan, weight target, or personalized risk score.
A borderline number can change with tape position, breathing, posture, and measurement tension. Repeat the measurement consistently rather than interpreting a hundredth as laboratory precision. The displayed ratio is rounded, while the half-height comparison uses the unrounded division.
Who should not use this result
The linked NHS tool says not to use it for a person under 5, during pregnancy, when an eating disorder is diagnosed or suspected, with a growth disorder or another condition affecting height, or for an adult whose BMI is over 35. People aged 17 or under should use it with a parent or carer, and the NHS asks parents or carers to check the child’s BMI first.
Do not use this page to diagnose a condition. If the exclusions apply, measurement is worrying, or you need advice, use an appropriate clinician or local health service. This page stores no profile and sends no entered measurements away from the browser.
Measurement examples and errors
Example one: waist 72 cm and height 168 cm gives about 0.43, so the waist is about 42.86% of height and below half. Example two: waist 94 cm and height 175 cm gives about 0.54, which is half or more. The statement is a comparison to the NHS public rule, not a conclusion about one disease.
Empty, negative, implausibly large, or waist-not-smaller-than-height entries are rejected. Clear removes the current inputs. When an empty field loses focus, its muted demonstration value returns; calculate only after replacing examples with your own consistent measurements.
Frequently asked questions
Is this waist-to-hip ratio? No. The denominator here is height, not hip circumference. Can I mix 80 cm with 68 inches? No; convert first or enter both in the same selected unit. Does 0.5 diagnose obesity? No. It is one screening comparison and the NHS says not to use the calculator to diagnose conditions. Does the result replace BMI? No; the NHS describes it as a measure used alongside BMI. Why is there no child risk category? The public guidance has age and parent/carer conditions; this page does not invent pediatric categories.