Why waist-to-height rather than BMI alone. BMI treats all weight as equal and cannot
see where it sits. Waist-to-height can, it needs no equipment beyond a tape measure, and
the same 0.5 threshold applies to both sexes and all ethnicities — including
people with high muscle mass, which is where BMI misleads most. NICE asks clinicians to record it
alongside BMI in adults with a BMI below 35.
Measuring it properly, because most of the error goes in here
- Find the midpoint between the bottom of your lowest rib and the top of your hip bone. That is usually just above the navel, and it is not where trousers sit.
- Stand relaxed and breathe out naturally. Do not hold your breath, and do not pull the tape tight enough to compress the skin.
- Tape level all the way round, parallel to the floor.
- Same conditions each time if you are tracking it — first thing in the morning, before eating, is the most reproducible.
- Measure height without shoes. An assumed height from memory is the commonest error in this calculation, and people are typically shorter than they think by their sixties.
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