Waist circumference
A measurement of abdominal girth, an indicator of visceral fat and a marker of cardiometabolic risk that is often more informative than BMI.
Waist circumference is measured halfway between the lowest rib and the top of the hip bone, at the end of a normal breath out, standing and without pulling the tape tight. This standardisation matters: measured at the navel or with the stomach pulled in, the figure loses all value.
The risk thresholds generally used are 94 cm for men and 80 cm for women for increased risk, and 102 and 88 cm for clearly high risk. They vary with ethnic origin, with South-East Asian populations showing risk at lower values.
It tells you about one specific type of fat, and this is what makes it valuable: visceral fat, the fat around the organs, behaves like an active tissue that releases inflammatory molecules. It is far more closely linked to cardiovascular risk and type 2 diabetes than the subcutaneous fat you can pinch between your fingers.
That is why it usefully complements BMI: two people with the same BMI can have very different risks depending on how their fat is distributed. Waist circumference is also one of the criteria for metabolic syndrome, and it responds quickly to changes in habits, often before the weight shown on the scales.