Calculate the Conicity Index to measure abdominal obesity independent of BMI. Uses waist circumference, weight, and height to assess metabolic risk.
The Conicity Index (C-Index) quantifies abdominal obesity by comparing a person's waist circumference to the circumference of a theoretical cylinder with the same height and weight. Developed by Valdez and colleagues in 1993, the index conceptualizes the human body shape as ranging from a perfect cylinder (C-Index = 1.0, meaning even fat distribution) to a double cone (C-Index approaching 1.73, indicating extreme central fat accumulation).
The formula normalizes waist circumference against body size, making it independent of BMI. This is important because two people with the same BMI can have very different fat distributions — one carrying fat predominantly around the abdomen (apple shape) and the other carrying it in the hips and thighs (pear shape). The Conicity Index captures this distinction, which BMI alone cannot.
Research has linked higher Conicity Index values to increased risk of cardiovascular disease, type 2 diabetes, hypertension, and metabolic syndrome. Several large-scale studies have found it to be a stronger predictor of these outcomes than BMI, making it a valuable complement to traditional weight-based assessments.
The Conicity Index measures fat distribution rather than total body mass, filling a gap that BMI leaves. Central (abdominal) fat is metabolically more dangerous than peripheral fat, and the C-Index specifically quantifies this pattern. It is particularly useful for individuals whose BMI falls in the normal range but who carry excess abdominal fat — the so-called "metabolically obese normal-weight" phenotype that BMI misses entirely.
Conicity Index = Waist (m) / (0.109 × √(Weight (kg) / Height (m))) The denominator represents the circumference of a cylinder with density 1.05 g/cm³ (close to water) and the same height and mass as the person. The constant 0.109 derives from: 2 × √(π / (1050 × 4)) ≈ 0.109. The index ranges from 1.0 (perfect cylinder) to approximately 1.73 (maximum conicity). Values above 1.25 for men and 1.18 for women generally indicate elevated abdominal obesity risk.
Result: Conicity Index = 1.263
An 85 kg person who is 178 cm tall with a 95 cm waist: C-Index = 0.95 / (0.109 × √(85 / 1.78)) = 0.95 / (0.109 × √47.75) = 0.95 / (0.109 × 6.910) = 0.95 / 0.7532 = 1.261. This exceeds the male threshold of 1.25, indicating above-average central fat accumulation and elevated metabolic risk.
The Conicity Index rests on an elegant geometric model. If a person's weight were distributed uniformly along their height, their body would resemble a cylinder, and their waist circumference would match the calculated cylinder circumference. As fat accumulates centrally, the body shape deviates from this cylinder toward a double cone, and the ratio of actual waist circumference to the cylinder's circumference increases.
Large cohort studies have consistently shown the Conicity Index to be a strong predictor of cardiometabolic risk. A 2018 meta-analysis of over 100,000 participants found that the C-Index predicted type 2 diabetes as well as waist circumference and better than BMI. In the ELSA-Brasil study involving 15,000 adults, the C-Index was among the top anthropometric predictors of hypertension and dyslipidemia.
BMI measures total body mass relative to height and cannot distinguish between peripheral and central fat deposition. Two individuals with identical BMIs — one apple-shaped and one pear-shaped — have vastly different metabolic risk profiles. The Conicity Index specifically quantifies this difference, making it a more targeted screening tool for the type of obesity most associated with disease.
Optimal C-Index cut-offs vary by ethnicity. South Asian and East Asian populations may have elevated risk at lower C-Index values due to inherent differences in body fat distribution. Conversely, athletes with well-developed core musculature may have higher waist measurements that inflate the C-Index without reflecting excessive fat. As with all anthropometric tools, clinical context is essential.
The Conicity Index (C-Index) is an anthropometric measure that quantifies how much a person's body shape deviates from a perfect cylinder. A cylindrical body (even fat distribution) has a C-Index near 1.0, while a cone-shaped body (central fat accumulation) has values approaching 1.73. It was proposed by Valdez et al. in 1993 specifically to detect abdominal obesity.
Commonly cited thresholds are below 1.25 for men and below 1.18 for women. However, optimal cut-offs may vary by ethnicity and population. Values above these thresholds indicate increased central fat accumulation and are associated with higher cardiovascular and metabolic disease risk.
Waist-to-hip ratio compares waist and hip circumferences but ignores height and weight. The Conicity Index normalizes waist circumference against a theoretical cylinder derived from height and weight, making it independent of body size. This allows more meaningful comparisons across individuals of different statures and weights.
Theoretically no. The maximum value is √3 ≈ 1.732, which would correspond to a body shape that is an infinitely thin double cone (all weight at the waist, no weight at the head or feet). In practice, observed values rarely exceed 1.40.
Yes. Multiple studies, including the Brazilian ELSA study and European EPIC cohort, have found the Conicity Index to be a significant predictor of cardiovascular events, often performing comparably to or better than BMI. Its advantage is that it specifically captures the abdominal fat pattern most strongly linked to cardiometabolic risk.
Very much so. The C-Index can identify "metabolically obese normal-weight" individuals — people with a healthy BMI but unhealthy abdominal fat distribution. These individuals are at elevated metabolic risk despite appearing lean by BMI standards. The C-Index captures this hidden risk.
Valdez, Seidell, Ahn, and Buchanan introduced the Conicity Index in a 1993 paper in the International Journal of Obesity. They based it on a mathematical model comparing the human torso to cylinders and cones of varying proportions.
Reducing waist circumference is the most direct approach. Regular aerobic exercise (30+ minutes most days) preferentially reduces abdominal fat. Dietary strategies emphasizing whole foods, lean protein, and reduced refined carbohydrates also help. Even a 2–3 cm reduction in waist measurement can noticeably improve the C-Index.