Calculate your Body Roundness Index (BRI) from your height and waist circumference and see which reference band your result falls into.
The Body Roundness Index (BRI) is a body-shape score calculated from just two measurements — your height and your waist circumference. It works by modelling your torso as an ellipse and estimating how "round" that ellipse is relative to your height, producing a single number that is generally used as a supplementary indicator of central body fat alongside measures like BMI and waist-to-height ratio. BRI was introduced in 2013 and is a newer metric with a smaller research base than long-established tools, so it works best as one extra data point rather than a stand-alone health verdict.
| Property | Value |
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BRI takes your waist-to-height ratio and runs it through a geometric formula that treats your torso as an ellipse, which is why the result behaves differently from a plain ratio like WHtR. Both measurements need to be in the same unit before you start, but because the ratio step cancels the units out, the final BRI number itself is unitless.
Rather than simply dividing waist by height the way WHtR does, BRI treats a cross-section through your torso as an ellipse, with your height standing in for one axis and your waist circumference used to estimate the other. The "e" value in the formula is the eccentricity of that ellipse — a measure of how stretched-out or how close to a circle the shape is. A smaller waist relative to height produces a more elongated, less circular ellipse and a lower BRI, while a larger waist relative to height pushes the shape closer to round and produces a higher BRI. This is the origin of the name "Body Roundness Index" — it is a geometric estimate of how round your midsection is, not a direct measurement of body fat.
| BRI | Category | What It Generally Indicates |
|---|---|---|
| Below 3.0 | Low / lean | Typical of a narrow, lean body shape |
| 3.0 – 4.44 | Below typical range | Leaner than the general adult average |
| 4.45 – 5.46 | Normal / typical range | Within the University Hospital Zurich (USZ) clinical reference range |
| 5.46 – 6.89 | Above typical range | Associated with increased visceral fat distribution |
| 6.9 and above | High | Linked to notably higher all-cause mortality risk in a 2024 cohort study |
These bands are drawn from more than one source: the sub-3.0 "low/lean" reference range comes from the original BRI research by Thomas et al. (2013), the 4.45–5.46 "normal/typical" band is the clinical reference range used by University Hospital Zurich, and the ≥6.9 "high" threshold reflects a 2024 JAMA Network Open cohort study that found this level of BRI was associated with up to a 49% higher all-cause mortality risk compared with a medium BRI of around 5. They are population-level reference bands, not individual diagnostic cut-offs.
Average BRI naturally rises with age in both sexes as body shape and fat distribution change over the lifespan. The figures below are population averages published by University Hospital Zurich and are provided for context only — they are not targets to aim for, and an individual reading below or above these averages is not automatically good or bad.
| Age Group | Men — Average BRI | Women — Average BRI |
|---|---|---|
| 18–29 | 2.91 | 2.61 |
| 30–39 | 3.54 | 3.13 |
| 40–49 | 3.92 | 3.67 |
| 50–59 | 4.21 | 4.25 |
| 60–69 | 4.35 | 4.61 |
| 70+ | 4.31 | 4.71 |
| Measure | Inputs Used | Limitation |
|---|---|---|
| BRI | Height + waist circumference, modelled as an ellipse | Newer metric with a smaller evidence base |
| WHtR | Height + waist circumference, as a simple ratio | Doesn't distinguish fat from muscle |
| BMI | Weight + height | Can't tell fat from muscle or where fat sits |
BRI and WHtR use the same two inputs, but BRI runs them through the ellipse formula above rather than a straight division, which is why the two scores use different scales and boundary values even though they are measuring a related concept. Neither BRI, WHtR, nor BMI is a diagnosis on its own — using more than one measure together, alongside professional medical advice, generally gives a more complete picture than relying on any single number.
Body Roundness Index estimates how round or elongated your torso is, using only your height and waist circumference as inputs. Two people with an identical waist measurement but different heights will generally have different BRI scores, because the formula scales the waist reading against height before converting it into an ellipse-based shape estimate. In practical terms, BRI is generally used as a proxy for central fat distribution — the same broad idea WHtR and waist circumference are used for — expressed through a geometric model rather than a straight-line ratio.
The researchers who introduced BRI in 2013 chose an ellipse model because the human torso is closer to an oval cross-section than a perfect circle, and they wanted a single score that reflected this shape rather than just a raw ratio of two measurements. Running WHtR through the eccentricity calculation compresses or stretches the resulting number in a non-linear way, which is why BRI values (typically in the low single digits) look nothing like WHtR values (typically 0.4–0.6) even though both are ultimately derived from the same two measurements.
BRI was first proposed by Thomas et al. in 2013 as an alternative way to estimate visceral fat without imaging equipment. Since then, a growing number of cohort studies have examined its relationship with health outcomes, including a widely cited 2024 JAMA Network Open study of US adults (Zhang et al.) that found a BRI of 6.9 or above was associated with up to a 49% higher risk of all-cause mortality compared with a medium BRI of around 5, and unusually low BRI values were also linked to elevated risk. University Hospital Zurich has incorporated BRI into its own clinical reference tools, using the 4.45–5.46 range as its typical adult band. Even so, BRI remains a younger metric overall, with a smaller and more recent body of supporting research than long-established tools like BMI and waist-to-height ratio.
It is tempting to assume that a lower BRI is always the healthier result, but this is not necessarily true, particularly later in life. As people age, natural loss of muscle mass and changes in body composition can lower waist circumference relative to height even when overall health is declining, which can pull BRI down without reflecting an improvement. For this reason, BRI results are best interpreted in context — alongside your age, muscle mass, and other health indicators — rather than read as a simple scale where lower always means better.
What counts as a good BRI?
There is no single BRI number that counts as good for everyone. University Hospital Zurich treats roughly 4.45 to 5.46 as the typical adult reference range, but average BRI shifts with age and sex — reference figures run from about 2.6 in younger adults up to the mid-4s in older adults. Rather than aiming for the lowest possible score, it is more useful to track your own BRI over time alongside other health measurements.
How is BRI different from BMI?
BMI is calculated from weight and height alone and does not indicate where on the body any extra weight is carried. BRI instead uses height and waist circumference to estimate how rounded your midsection is relative to your height, which puts more focus on central body shape than overall size. Because they capture different information, many researchers suggest looking at BMI and BRI together rather than relying on either one alone.
How is BRI different from waist-to-height ratio?
Waist-to-height ratio (WHtR) is a straightforward division of waist circumference by height, so equal changes in WHtR mean the same thing at any starting point. BRI takes that same waist-to-height ratio and runs it through a geometric formula that models the torso as an ellipse, producing a curved rather than straight-line score. In practice this means BRI tends to increase more sharply than WHtR as waist circumference grows relative to height.
Does BRI apply to athletes or muscular people?
BRI is calculated purely from waist circumference and height, so it does not directly measure muscle mass the way body fat percentage or a DEXA scan does. A muscular person with a naturally broad frame can still show a moderate or elevated BRI even at low body fat levels, particularly if their waist is proportionally wide. As with BMI, BRI is best treated as one data point rather than a complete picture of body composition for people who train heavily.
How do I measure my waist circumference correctly for a BRI reading?
Measure at the narrowest point of your torso, usually roughly level with your belly button, after breathing out normally and with the tape held horizontal and snug against the skin without compressing it. Measure your height without shoes, standing upright against a flat wall or vertical surface. Taking two or three readings of each measurement and averaging them will make your BRI result more reliable.
Is BRI clinically validated?
BRI is a relatively new research metric, first proposed in 2013, and it has a smaller body of supporting evidence than long-established measures such as BMI or waist-to-height ratio. Since then, cohort studies — including a 2024 JAMA Network Open analysis of US adults — have linked higher BRI values to increased health risks, and University Hospital Zurich uses BRI as one of its clinical reference tools. It is best treated as a supplementary indicator rather than a stand-alone diagnostic test.
Can BRI change quickly?
Yes. Because BRI is driven mainly by waist circumference, factors such as recent meals, bloating, hydration, and measurement technique can shift the score from one reading to the next. For a more meaningful picture, measure under similar conditions each time, such as first thing in the morning, and look at the trend over several weeks or months rather than any single reading.
What are the main limitations of BRI?
BRI is calculated from only two measurements, so it cannot account for muscle mass, bone density, fat distribution beyond the waist, or overall health status. It is a relatively young metric with less long-term research behind it than BMI or waist-to-height ratio, and a very low BRI in older adults can reflect underweight or muscle loss rather than a favourable body shape. It should be treated as one supplementary indicator alongside other measurements and professional medical advice, not as a diagnosis on its own.