By Zencalcy Editorial TeamLast reviewed About us
Body Roundness Index (BRI) turns waist circumference and height into a single number that describes how round the torso is. It was introduced as an alternative to BMI that captures abdominal fat without needing weight. Higher values indicate a rounder, more centrally weighted body.
Measure body roundness from waist and height.
BRI = 364.2 − 365.5 × √(1 − (waist ÷ 2π)² ÷ (0.5 × height)²)
Waist and height must be in the same units. Thomas et al. (2013) derived the index from an ellipse model of the torso. There are no universally agreed cutoffs; published studies often divide BRI into quintiles within a population.
| Symbol | Meaning |
|---|---|
| BRI | Body Roundness Index; higher values indicate a rounder torso. |
| waist | Waist circumference, same unit as height. |
| height | Standing height. |
Waist ÷ 2π = 13.53 cm. Half the height is 87.5 cm. The ratio squared is 0.0239, so the square root is 0.988. BRI = 364.2 − 365.5 × 0.988 = 3.1, a mid-range value.
BRI treats the torso as an ellipse and asks how wide the waist is relative to the height of that ellipse. A perfectly cylindrical body with a waist equal to its height would score high; a narrow waist relative to height scores low. In practice, the index behaves like a curved version of waist-to-height ratio, giving more weight to large waist values. That curvature is why BRI can separate people who look similar on a simple ratio. Its weakness is the same as any tape-based index: measurement error at the waist propagates into the result, and the equation was fitted to a specific population. Use BRI as a companion to waist-to-height rather than a replacement, and always take repeated measurements at the same landmark to see a real trend rather than noise.
Continue with the ABSI Calculator (A Body Shape Index), Adjusted Body Weight Calculator, or the BAI Calculator (Body Adiposity Index) — or browse more body measurements tools and all health calculators.
Also see the Body Fat Calculator.
There is no single clinical cutoff. Studies often report higher BRI as associated with greater cardiometabolic risk, and some propose ranges around 1–3 as lower risk and above 5 as higher risk, but these are research thresholds rather than guidelines.
Every result is a screening estimate from published anthropometric equations, not a diagnosis or a measurement of body composition. Tape measurements should be taken snugly against the skin without compressing it, at the landmarks named in each tool. Equations were derived in specific populations and can be less accurate for athletes, older adults, children, pregnant people and people with significant oedema.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026