Last updated: 2026-06-22

Conicity Index

The conicity index (C-index) describes body shape from three measurements: waist circumference, weight, and height. It was introduced by Rafael Valdez in 1991 as a model-based index of abdominal adiposity. The index compares the actual waist to the waist a reference cylinder of the same height and volume would have, producing a single number that reflects how much fat is carried around the middle relative to body size.

What the index represents

The model imagines an idealised body with no central fat as a plain cylinder. Its height matches the person's height, and its volume matches the person's volume, inferred from weight. Such a cylinder has a definite waist circumference. A real body with abdominal fat tapers outward at the middle and inward toward the limbs, so its waist is larger than the cylinder's. The conicity index is the ratio of the two: how many times wider the real waist is than the cylinder's waist. A value near 1 corresponds to a nearly cylindrical build, while values approaching 1.5 describe a more pronounced double-cone shape with central fat.

The formula

Here $\mathrm{WC}$ is the waist circumference in metres, $w$ is weight in kilograms, and $h$ is height in metres. The term in the denominator is the waist circumference of the reference cylinder. The constant 0.109 carries the unit conversion: it follows from the geometry of a cylinder together with an assumed average body density, so that the denominator comes out in metres when weight is in kilograms and height is in metres.

Worked example

Consider an adult with a waist of 85 cm33 in, a weight of 70 kg154 lb, and a height of 175 cm69 in. Working in metres and kilograms:

A value near 1.23 sits in the moderate band, reflecting a waist that bulges modestly beyond the cylindrical reference.

Interpreting the number

There is no single clinical cut-off for the conicity index. The bands shown alongside the result treat values below about 1.18 as low, 1.18 to 1.25 as moderate, and above 1.25 as higher, but the thresholds that best separate risk groups differ by population, sex, and age. Studies have linked higher values to greater abdominal fat and cardiometabolic risk. For an individual, the trend across several measurements usually says more than one reading against population averages.

Limits

The index is a geometric approximation, not a body-fat measurement. It assumes the body behaves like a smooth cylinder of uniform density and takes no account of muscle, bone, frame, or the difference between subcutaneous and visceral fat. It is best used alongside other measures such as the Waist-to-Height Ratio Calculator and the Waist-to-Hip Ratio Calculator, and any health decision should rest on a professional assessment rather than a single index.