Waist-to-height ratio

The formula

• WHtR = w / h

w is the waist circumference and h the height, in the same unit; the ratio has none. The rule of thumb that goes with it, keep your waist to less than half your height, is the ratio below 0.5.

A worked example

A waist of 80 cm on a height of 170 cm: WHtR = 80 / 170 = 0.47, under the boundary. A waist of 95 cm on the same height is 0.56. Turned round, half of 170 cm is 85 cm: the waist at which this person reaches 0.5.

The boundary of 0.5

Ashwell and Hsieh (2005) proposed 0.5 as a single boundary for men and women, adults and children, above which the risk of the conditions linked to abdominal fat rises; the source is cited under the formula. It is a screening threshold from population studies, and a person at 0.52 is not ill nor one at 0.48 well. The measure says where the fat sits, which the scales do not.

Against BMI

BMI divides weight by height squared and cannot tell muscle from fat or a waist from a chest. The waist-to-height ratio is a tape measure’s answer to the same question and needs no scale. The waist–hip ratio is the other tape measure, dividing by the hip instead; the body measurements calculator works out all three.

Common mistakes

• Measuring the waist at the belt. The protocol is midway between the lowest rib and the top of the hip bone, at the end of a normal breath out.
• Mixing units. Centimetres over centimetres or inches over inches; the ratio is the same either way.
• Reading it as a diagnosis. It is a screening figure, and not medical advice.

Frequently asked questions