Body Roundness Index calculator
Enter your height and waist measurement to see the Body Roundness Index from the 2013 Thomas equation, to two decimals. A shape index with no category attached, and it runs entirely in your browser.
Medically reviewed by Kevin Brandstetter, M.D.Updated September 28, 2026
The paper measured the waist above the top of the hip bone (the iliac crest). Keep the tape level with the floor.
Your Body Roundness Index
Enter your height and waist
The index appears here once both are filled in.
A calculation, not a diagnosis.
The Body Roundness Index models the body as an ellipse drawn from two measurements, height and waist. It describes body shape and says nothing on its own about health, fitness, or any condition, and this page attaches no category or range to it. This tool is for adults. A licensed clinician reads a body measurement alongside your history, not instead of it.
Methodology
- How this is calculated
- The body is treated as an ellipse whose long axis is your height and whose short axis comes from your waist circumference divided by pi. Its eccentricity is the square root of 1 minus (waist ÷ 2π)² ÷ (height ÷ 2)², and the index is 364.2 − 365.5 × eccentricity. Height and waist enter in the same unit, so inches and centimeters give the same answer. The result is shown to two decimals.
- Where the data comes from
- Thomas DM, Bredlau C, Bosy-Westphal A, et al., Relationships between body roundness with body fat and visceral adipose tissue emerging from a new geometrical model, Obesity 2013;21(11):2264–2271, doi:10.1002/oby.20408. The axes and the index come from the paper's methods. The written-out eccentricity term is in the paper's online supplement, which this page could not retrieve; the term above is the standard eccentricity of an ellipse with those axes. The paper measured the waist in the NHANES III survey, above the iliac crest.
- Last updated
- September 28, 2026
- What this does not account for
- Weight, body composition, age, sex, ethnicity, pregnancy, and every other fact a clinician weighs. The paper's authors also published an online calculator that shades a range by age and height; that range was not published as a table, so this page does not reproduce it and gives no category.
What the numbers looked like
The paper computed the index for adults in the US NHANES III survey. Its text reports a lowest observed value of 1 and a highest of 16, and its Table 3 lists values up to 18.09 among men with a BMI of 40 or more. The table below reproduces the ranges and means from Table 3 by BMI group and sex. They describe that survey population, not a target for any one person.
| BMI group | Men, range (mean) | Women, range (mean) |
|---|---|---|
| 40 or more | 6.80 to 18.09 (10.00) | 5.80 to 14.84 (9.87) |
| 30 to under 40 | 3.15 to 10.74 (6.47) | 3.83 to 12.29 (6.86) |
| 25 to under 30 | 2.03 to 7.33 (4.66) | 2.34 to 11.53 (4.96) |
| 18.5 to under 25 | 1.23 to 6.62 (3.07) | 1.57 to 6.85 (3.28) |
| Under 18.5 | 1.00 to 3.36 (1.76) | 1.27 to 4.05 (1.95) |
| All | 1.00 to 18.09 (4.64) | 1.27 to 14.84 (5.16) |
Source: Thomas and colleagues, 2013, Table 3. The table's standard deviation column is left out because two of its entries are evidently misprinted.
Why a shape index
BMI uses height and weight, so two people with the same BMI can carry weight very differently. The Body Roundness Index uses height and waist instead, which is why the paper studied it alongside measured body fat. Higher values describe a rounder shape and values near 1 a narrower one.
Nothing here is stored
Your answers stay in your browser. They are not sent to Temi, not saved, not attached to you, and not recorded in any session replay, and closing the tab clears them. Temi knows only that someone opened this tool, the same thing it knows about every page.
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