Conicity Index
Page updated: Evidence reviewed: What this means
Conicity Index compares measured waist circumference with the circumference expected from a cylinder of the same height and weight, using the Valdez (1991) formula. A value near 1 indicates a waist close to the cylindrical reference; higher values indicate a larger waist relative to that reference.
These percentiles were derived from NHANES data for 18,716 US adults aged 20 and over after excluding participants recorded as pregnant. The pooled table spans survey periods from 2015 through 2023 and is a period reference, not a claim about a single current population. The methodology page documents the formula, exclusions, duration-adjusted weights, and sensitivity check.
How to Perform This Test (Protocol)
- Equipment
-
- Flexible non-stretch anthropometric tape
- Stadiometer or other accurate height measure
- Calibrated scale
- Protocol Steps
-
- Stand upright with feet together, arms relaxed at the sides, and abdomen relaxed.
- Measure waist circumference at the high point of the iliac crest, with the tape horizontal and not compressing the skin. Record at the end of a normal expiration. This is the NHANES measurement site used for these percentiles.
- Measure standing height in metres and body weight in kilograms.
- Calculate CI = waist_m ÷ (0.109 × √(weight_kg ÷ height_m)).
- Scoring
Compare the result with the table for your sex and age bracket. The percentile describes position in this NHANES distribution; it is not a diagnosis or universal risk category.
- Notes
Waist sites are not interchangeable. A measurement taken at the WHO midpoint between the lowest rib and iliac crest should not be compared directly with these NHANES iliac-crest percentiles.
Data source: NHANES (CDC), derived Conicity Index percentiles About this study
Reference population: US adults aged 20 and over from NHANES survey periods spanning 2015-2023 after excluding participants recorded as pregnant, nationally representative
Conicity Index Norms Chart by Age and Sex (index)
| Age | Sex | Percentile | ||||
|---|---|---|---|---|---|---|
| 5th | 25th | 50th | 75th | 95th | ||
| 20-24 | Male | 1.107 | 1.170 | 1.229 | 1.297 | 1.384 |
| Female | 1.100 | 1.169 | 1.221 | 1.281 | 1.395 | |
| 25-29 | Male | 1.124 | 1.191 | 1.248 | 1.307 | 1.403 |
| Female | 1.123 | 1.189 | 1.243 | 1.315 | 1.418 | |
| 30-34 | Male | 1.152 | 1.225 | 1.277 | 1.339 | 1.420 |
| Female | 1.135 | 1.202 | 1.267 | 1.339 | 1.437 | |
| 35-39 | Male | 1.174 | 1.247 | 1.299 | 1.346 | 1.433 |
| Female | 1.148 | 1.221 | 1.272 | 1.342 | 1.447 | |
| 40-44 | Male | 1.190 | 1.266 | 1.306 | 1.354 | 1.436 |
| Female | 1.165 | 1.232 | 1.289 | 1.347 | 1.437 | |
| 45-49 | Male | 1.190 | 1.273 | 1.314 | 1.361 | 1.451 |
| Female | 1.173 | 1.228 | 1.286 | 1.356 | 1.443 | |
| 50-54 | Male | 1.206 | 1.285 | 1.331 | 1.374 | 1.462 |
| Female | 1.182 | 1.256 | 1.320 | 1.373 | 1.459 | |
| 55-59 | Male | 1.225 | 1.297 | 1.342 | 1.388 | 1.464 |
| Female | 1.177 | 1.271 | 1.326 | 1.384 | 1.468 | |
| 60-64 | Male | 1.244 | 1.304 | 1.357 | 1.413 | 1.488 |
| Female | 1.187 | 1.279 | 1.335 | 1.389 | 1.455 | |
| 65-69 | Male | 1.248 | 1.314 | 1.364 | 1.412 | 1.480 |
| Female | 1.212 | 1.286 | 1.348 | 1.409 | 1.479 | |
| 70-74 | Male | 1.260 | 1.339 | 1.381 | 1.429 | 1.492 |
| Female | 1.235 | 1.307 | 1.355 | 1.414 | 1.475 | |
| 75-79 | Male | 1.281 | 1.345 | 1.392 | 1.440 | 1.512 |
| Female | 1.220 | 1.301 | 1.356 | 1.415 | 1.503 | |
| 80+ | Male | 1.280 | 1.350 | 1.398 | 1.440 | 1.507 |
| Female | 1.226 | 1.313 | 1.363 | 1.421 | 1.498 | |
What to expect by age group
Median Conicity Index rises from about 1.22 in the youngest brackets to about 1.40 in the oldest bracket. Male medians are higher than female medians in every age bracket in this dataset. The labels run from Very low to Very high because they describe a population distribution, not good-to-bad performance or clinical risk.
| Age | Males | Females |
|---|---|---|
| 20-24 | 1.170 to 1.297 | 1.169 to 1.281 |
| 25-29 | 1.191 to 1.307 | 1.189 to 1.315 |
| 30-34 | 1.225 to 1.339 | 1.202 to 1.339 |
| 35-39 | 1.247 to 1.346 | 1.221 to 1.342 |
| 40-44 | 1.266 to 1.354 | 1.232 to 1.347 |
| 45-49 | 1.273 to 1.361 | 1.228 to 1.356 |
| 50-54 | 1.285 to 1.374 | 1.256 to 1.373 |
| 55-59 | 1.297 to 1.388 | 1.271 to 1.384 |
| 60-64 | 1.304 to 1.413 | 1.279 to 1.389 |
| 65-69 | 1.314 to 1.412 | 1.286 to 1.409 |
| 70-74 | 1.339 to 1.429 | 1.307 to 1.414 |
| 75-79 | 1.345 to 1.440 | 1.301 to 1.415 |
| 80+ | 1.350 to 1.440 | 1.313 to 1.421 |
Detailed Breakdowns
Select an age group and sex below for detailed percentile charts and distribution labels.
Frequently Asked Questions
What is a normal Conicity Index?
In this NHANES analysis, the median ranges from about 1.22 in younger adults to about 1.40 in the oldest bracket. The percentile tables show how a value ranks within the same sex and age group. They do not define a universal healthy or clinical range.
How is Conicity Index different from waist-to-height ratio?
Both use the waist, but Conicity Index also factors in body weight: it compares your waist to the circumference of a cylinder with the same weight and height (Valdez 1991), whereas waist-to-height ratio is simply waist divided by height. Conicity is reported on a shape-index scale around 1.1 to 1.5 rather than a 0-1 ratio.
Why do these percentiles use a Very low to Very high scale?
Conicity Index is a body-shape distribution, not a fitness test. Published thresholds vary by study, population, and outcome, so the tables show relative position in the sampled population rather than labelling values good or bad.
Can I compare these percentiles with another population?
Use caution. These percentiles come from US adults measured in NHANES and pooled across survey periods from 2015 through 2023. Differences in population, waist-measurement site, age distribution, and survey period can all affect comparisons.