About the Body Roundness Index Calculator
The Body Roundness Index (BRI) describes how round your body is, using only your waist circumference and height. It was developed in 2013 by Diana Thomas and colleagues, who modelled the body as an ellipse: the rounder the ellipse, the higher the index. Unlike BMI, BRI ignores weight entirely and focuses on abdominal shape, which tracks visceral fat — the fat around organs that is most closely linked to heart disease and type 2 diabetes.
Enter your height and waist in inches or centimetres to get your BRI, its risk band, and the waist range that would place you in the band associated with the lowest risk for your height. Most adults score between about 1 and 10.
The bands come from a 2024 study of nearly 33,000 US adults in NHANES (Zhang et al., JAMA Network Open), which found a U-shaped link with all-cause mortality: risk was lowest for a BRI of about 4.5 to 5.5, 25% higher below 3.4 and 49% higher at 6.9 or above. BRI is a research and screening measure, not a diagnosis, and has not yet been adopted in clinical guidelines.
With the default inputs, the body roundness index (bri) is 3.63. Change any value above to recalculate instantly.
How to use the body roundness index calculator
- 1Choose US or metric units and enter your height.
- 2Measure your waist midway between the lowest rib and the hip bone after breathing out.
- 3Enter the waist measurement.
- 4Read your BRI and its risk band.
- 5Compare your waist with the range that gives a BRI of 4.5–5.5 for your height.
Formula and method
Thomas and colleagues modelled the human body as an ellipse whose long axis is height and whose short axis is the diameter implied by the waist circumference (WC ÷ π). The square-root term is the eccentricity of that ellipse: close to 1 for a tall, slim shape and smaller for a rounder one. The constants 364.2 and 365.5 rescale eccentricity onto a convenient range of roughly 1 to 16.
Waist and height must use the same unit, so the result is unit-free. The waist range for the lowest-risk band is found by reversing the formula for BRI values of 4.5 and 5.5 at your height.
- BRI
- Body Roundness Index
- WC
- Waist circumference
- H
- Height, in the same unit as WC
Worked examples
5 ft 10 in with a 36-inch waist
Height is 70 in. (36 ÷ 2π)² ÷ 35² = 0.0268, so √(1 − 0.0268) = 0.98651 and BRI = 364.2 − 365.5 × 0.98651 ≈ 3.63 — in the lower-middle band, just under the 4.5–5.5 range.
Metric: 165 cm with a 98 cm waist
(98 ÷ 2π)² ÷ 82.5² = 0.03574, √(1 − 0.03574) = 0.98197, so BRI = 364.2 − 365.5 × 0.98197 ≈ 5.29 — inside the 4.5–5.5 band linked to the lowest risk.
6 ft with a 44-inch waist
At 72 in, (44 ÷ 2π)² ÷ 36² = 0.03784, giving BRI ≈ 5.68. Reversing the formula shows a 43.4-inch waist would give exactly 5.5 at this height, so trimming about 0.6 in would reach the lowest-risk band.
Frequently asked questions
What is a healthy body roundness index?+
There is no official cut-off yet. In a 2024 study of US adults, the lowest risk of death was seen with a BRI of about 4.5 to 5.5; risk was 25% higher below 3.4 and 49% higher at 6.9 or above.
Is BRI better than BMI?+
BRI captures abdominal fat, which BMI cannot, and predicts visceral fat slightly better in the original study. But BMI has decades of evidence and clinical cut-offs. Using both — or BMI plus waist-to-height ratio — gives a fuller picture.
How do I measure my waist for BRI?+
Stand upright, find the point midway between your lowest rib and the top of your hip bone, wrap the tape level around your body and read it after a normal breath out. Do not pull the tape tight.
Why does BRI not use my weight?+
BRI is a shape index. It estimates how round your torso is relative to your height, which reflects central fat. Two people with the same weight can have very different BRIs depending on where they carry fat.
How is BRI related to waist-to-height ratio?+
Both use only waist and height, and they rise together: a waist-to-height ratio of 0.5 corresponds to a BRI of about 3.4, and 0.6 to about 5.4. BRI stretches the scale so differences among larger waists are easier to see.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.