Body Roundness Index (BRI): What It Is and How It Compares to BMI — 2026

The Body Roundness Index, usually shortened to BRI, is a body-shape measure introduced by Thomas and colleagues in a 2013 paper in the journal Obesity. Where BMI uses only weight and height, BRI uses waist circumference and height. It models the torso as an ellipse and turns that shape into a single number, so a higher BRI means a rounder, more apple-shaped body. The goal was to capture abdominal fat, especially the visceral fat packed around the organs, which BMI cannot see.

In the original study, BRI predicted percentage body fat and visceral adipose tissue a little better than BMI, waist circumference, or hip circumference on their own. It was offered as a visual, screening-style tool rather than a diagnostic test. Importantly, BRI is a research metric and is not an official CDC or WHO standard the way the adult BMI categories are.

With waist circumference and height measured in meters, the formula is: BRI = 364.2 minus 365.5 times the square root of (1 minus ((waist divided by 2 pi) squared divided by (0.5 times height) squared)). In compact form: BRI = 364.2 - 365.5 x square root of (1 - ((WC / 2 pi) squared / (0.5 x Height) squared)).

In practice the number is small and positive. Published work describes BRI values that commonly run from about 1 up to roughly 16 in adult populations, with higher values indicating a rounder shape. The exact waist site matters: most research measures at the level of the navel, the same general landmark used for waist-circumference risk assessment.

A 2024 study in JAMA Network Open (Zhang and colleagues) examined BRI in 32,995 US adults drawn from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2018. Mean BRI rose from 4.80 to 5.62 over those two decades, a small but steady increase. Over a median follow-up of about 10 years, the study found a U-shaped link with all-cause mortality: compared with the middle band (BRI about 4.5 to 5.5), adults with a BRI below 3.4 had about 25 percent higher risk and those with a BRI of 6.9 or above had about 49 percent higher risk.

Other studies have reported similar themes. A 2025 Scientific Reports analysis of US adults aged 65 and older linked higher BRI to higher all-cause mortality, and a 2020 systematic review in Obesity Reviews found BRI useful for predicting metabolic syndrome. Across this body of work, the consistent message is that body shape, not just weight, carries health signal.

BMI is weight divided by height squared, so it treats a pound of muscle and a pound of fat the same. BRI swaps weight for waist circumference, which is why it responds to abdominal fat that BMI misses. Two people with the same BMI can have very different BRI values if one carries fat around the middle and the other carries it on the hips and thighs.

That makes BRI a closer cousin to waist-to-height ratio and waist-to-hip ratio than to BMI. The trade-off is familiarity and official backing: BMI has decades of public-health use and fixed CDC and WHO categories, while BRI is newer and its risk thresholds are still being studied across different populations.

BRI is one of several newer shape indices. Waist-to-height ratio keeps the simple rule of thumb that your waist should stay below half your height. A Body Shape Index (ABSI) adjusts waist circumference for both BMI and height. BRI stands out because it explicitly models the body as an ellipse and was built to track visceral fat. None of these replaces the others; they are different lenses on the same question of where fat is stored.

For everyday use, waist circumference and waist-to-height ratio remain the simplest, best-documented companions to BMI. BRI is worth knowing because research increasingly shows that fat distribution, not just total weight, drives cardiometabolic risk.

BRI is a screening research tool, not a diagnosis. Its risk cut points are not yet standardized the way adult BMI categories are, and healthy BRI bands differ between studies, so a single number should not be read as good or bad on its own. Like any tape-measure metric, BRI depends on consistent technique: measuring at the wrong spot or pulling the tape tight changes the result.

BRI also shares one limitation with BMI: because it is built from a waist and a height, a very muscular person with a large waist can score higher than their low body fat would suggest. It does not replace a clinical assessment, blood work, or a conversation with a healthcare professional.

For most people, BMI plus waist circumference and waist-to-height ratio already cover the ground BRI addresses, using methods backed by CDC and WHO references. BRI is interesting if you like following the research, but it should be treated as supplementary information rather than a target to chase. If a shape-based measure raises a flag for you, bring it to a clinician who can weigh it against your full health picture.

As with all body metrics on this site, BRI is educational. It is not a substitute for personalized medical advice, and any number that affects a health decision should be interpreted by a qualified professional.

This article cites peer-reviewed research and official references. All sources were retrieved on 2026-08-15.

• Thomas DM, 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. PMC: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3692604/
• Zhang X, et al. Body Roundness Index and All-Cause Mortality Among US Adults. JAMA Netw Open. 2024;7(6):e2415051. DOI: 10.1001/jamanetworkopen.2024.15051. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2819558
• Prognostic effect of body roundness index on all-cause mortality among US older adults. Scientific Reports. 2025;15:17843. https://www.nature.com/articles/s41598-025-02598-4
• Rico-Martin S, et al. Effectiveness of body roundness index in predicting metabolic syndrome: a systematic review and meta-analysis. Obesity Reviews. 2020;21(7):e13023.