In more detail
The WHO protocol measures the waist midway between the lowest rib and the top of the hip bone, and the hips around the widest part of the buttocks, standing relaxed at the end of a normal breath out. The WHO defines abdominal obesity as a ratio above 0.90 in men and above 0.85 in women, a marker of increased metabolic risk; cut-offs differ between populations, so treat them as a guide. The waist-to-height ratio, waist divided by height, is a related measure for which under 0.5 is often suggested.
Why it matters
Fat stored around the abdomen is more strongly linked with type 2 diabetes and heart disease than fat on the hips and thighs, so the ratio can flag risk in people whose BMI (body mass index) looks normal. Small differences in where the tape sits change the result by a few hundredths, so measure the same way each time. It is a screening number, not a diagnosis; discuss concerns with a health professional.
Example
Waist 82 cm, hips 100 cm: 82 / 100 = 0.82
Man, waist 95 cm, hips 98 cm: 0.97 (above 0.90)
Woman, waist 88 cm, hips 97 cm: 0.91 (above 0.85)
Waist-to-height, 82 cm at 170 cm: 0.48
Common confusion
The ratio says where fat is carried, not how much there is; for the amount see Body fat percentage.