Waist Circumference, Waist-to-Height and Waist-to-Hip Ratio Explained

Why where fat is carried matters

Body mass index compares weight with height and says nothing about where the weight sits. Two people with the same BMI can have very different amounts of fat around the abdomen, and that difference is clinically relevant: fat stored in and around the abdominal organs, often called central or visceral adiposity, is more strongly associated with cardiometabolic risk than fat stored in the hips and thighs.

That is the reasoning behind measuring the waist. A tape measure cannot distinguish visceral fat from subcutaneous fat, so every waist-based number is an indirect marker, but it is a cheap and reproducible one that adds information BMI lacks. It is also one of the few body measurements most people can take accurately at home.

How to measure correctly

Technique changes the number, and the published cut-points assume a particular protocol. The World Health Organization expert consultation on waist circumference and waist-hip ratio sets out a standard method, and a measurement taken differently is not comparable to its thresholds.

1. Stand upright, feet together, arms relaxed at your sides, and breathe normally.
2. Find the midpoint between the lowest rib and the top of the hip bone (the iliac crest) at the side of the body.
3. Wrap a flexible, non-stretch tape measure around the body at that level, snug but not compressing the skin, and keep it parallel to the floor.
4. Take the reading at the end of a normal, relaxed exhalation, not while holding your breath or pulling the stomach in.
5. For the hip measurement, measure around the widest part of the buttocks, again with the tape level.
6. Measure twice. If the two readings differ by more than about a centimeter, measure a third time.

Measuring over clothing, at a different level from the standard, or in the evening after a large meal will all shift the number. For tracking over time, the most important thing is to measure the same way each time, at roughly the same time of day.

Three measurements and what each says

Waist circumference, waist-to-hip ratio and waist-to-height ratio all target central fat but through different arithmetic, and each has its own strengths.

Waist circumference is the simplest: one measurement, no arithmetic. Its drawback is that it ignores height, so the same waist means different things in a short person and a tall one, and it requires separate cut-points for men and women, and in practice for different ethnic groups.

Waist-to-hip ratio divides the waist by the hip measurement, and so captures body shape: a higher value means proportionally more fat at the waist than at the hips. The hip measurement adds a second source of error and the ratio can obscure a large waist in someone who also has large hips.

Waist-to-height ratio divides the waist by height. It adjusts for body size without a hip measurement, and because the NICE bands use the same values for men and women of different heights, it is the easiest to remember: a waist less than half of your height falls in the lower band.

A worked example

Consider an adult woman who is 165 centimeters tall with a waist of 84 centimeters and hips of 100 centimeters. Her waist-to-height ratio is 84 divided by 165, which is 0.51, within the NICE band described as increased central adiposity. Her waist-to-hip ratio is 84 divided by 100, which is 0.84, just under the WHO cut-point of 0.85. Her waist circumference of 84 centimeters is above the WHO lower threshold of 80 centimeters for women and below the upper threshold of 88.

Three measurements, three slightly different readings of the same body. That is not a contradiction: the measures use different thresholds, built from different populations and endpoints, and none of them is a diagnosis. What the example shows is why it is worth looking at more than one, and why none of the three should be treated as a verdict.