Conicity Index Calculator (C Index)

The conicity index scores how far your torso has drifted from a cylinder toward a double cone. It needs three inputs — waist, weight and height — and no hip measurement, which is what separates it from every other shape ratio. Enter your numbers below.

How the geometry works

Ronald Valdez proposed the index in 1991 on a simple premise: for a given weight and height, assuming a constant body density, there is an expected waist. Compare the real waist to the expected one and you have a dimensionless score.

C index = waist in meters ÷ (0.109 × √(weight in kg ÷ height in m))

Someone with almost no abdominal accumulation approaches a cylinder and scores near 1. As fat concentrates at the middle while the limbs stay narrow, the silhouette becomes two cones joined at the waist and the score rises. A 200 lb, 5 ft 10 in adult (91 kg, 1.78 m) with a 38 in (97 cm) waist scores about 1.25.

What the thresholds are worth

This is the part most calculators skip. The values you will see quoted — 1.25 for men and 1.18 for women — were proposed by Pitanga and colleagues and were derived in Brazilian populations. They are reproduced widely in the literature, including in the Einstein São Paulo study cited below, but no United States agency has adopted a conicity cut-off, and the index has not been calibrated on a US sample.

Read your score accordingly: as a position on a continuum, not as a pass or fail. A number that moves from 1.30 to 1.22 over a year of changed habits tells you something real. A number sitting at 1.19 tells you very little about whether you personally are at risk.

C index	How to read it
Below about 1.2	Waist close to the cylinder predicted by your size
About 1.2 to 1.3	Measurable central accumulation
Above about 1.3	Pronounced double-cone shape

What has a US number behind it

If you want an abdominal measurement with an American threshold attached, use the raw waist. The NHLBI flags more than 40 inches (102 cm) in men and more than 35 inches (89 cm) in women as raising the risk of heart disease and type 2 diabetes — a single measurement, no arithmetic, and a cut-off issued by a US institute.

The WHO route is the waist-to-hip ratio, at 0.90 for men and 0.85 for women, which describes distribution rather than amount. And if what you want is the share of your body that is fat rather than the shape it makes, that is a different measurement entirely — start at the body fat percentage calculator.

Every one of these is a screen. A high value is a reason to have a conversation with a clinician, not a diagnosis by itself.