What is Body Roundness Index?

Body Roundness Index (BRI) is a body-shape estimate calculated from waist circumference and height, using a geometric model of an ellipse fitted to the body. It was introduced in 2013 as an alternative way to estimate central body fat without needing weight.

What is a good BRI score?

Lower BRI values generally correspond to a body shape that is less waist-dominant. Reference bands are based on the original validation study’s population quartiles — see the table below — but BRI is newer than BMI and its interpretation is still an active area of research.

Is BRI better than BMI?

BRI directly incorporates waist circumference, so it captures fat distribution that BMI misses entirely. Whether it out-predicts other waist-based measures like waist-to-height ratio for a given health outcome is still being studied — it is one more tool in the picture, not a replacement for all others.

Why doesn’t BRI need my weight?

BRI models the body as an ellipse using only waist circumference and height, so weight isn’t a required input. This makes it usable even when weight isn’t known or trusted, though it also means it cannot capture information that weight alone would add.

Body Roundness Index Calculator

Body Roundness Index (BRI) estimates body shape from waist circumference and height alone — no weight required. It models the body as an ellipse to estimate central body fat, a newer alternative to BMI introduced in 2013.

Calculate your BRI

Enter metric measurements. Runs entirely in your browser.

The BRI formula

BRI = 364.2 − 365.5 × √(1 − (waist ÷ 2π)² ÷ (0.5 × height)²)

Waist and height must be in the same unit. The formula treats the body's cross-section as an ellipse and derives its eccentricity from the two measurements.

BRI reference bands

Body roundness index bands
BRI	Band
–3.41	Very low
3.41–4.45	Low
4.45–5.46	Moderate
5.46–6.91	High
6.91+	Very high

These bands come from the original validation study's reference population and are an emerging research tool, not a settled clinical cutoff the way BMI categories are treated.

How to use BRI

BRI is newer and less studied than BMI, so treat it as one additional data point alongside other measures, not a replacement for all of them. Measure your waist consistently — around the navel, standing relaxed — so results are comparable over time, and discuss any health concern with a healthcare provider.

Common questions

What is Body Roundness Index?: Body Roundness Index (BRI) is a body-shape estimate calculated from waist circumference and height, using a geometric model of an ellipse fitted to the body. It was introduced in 2013 as an alternative way to estimate central body fat without needing weight.
What is a good BRI score?: Lower BRI values generally correspond to a body shape that is less waist-dominant. Reference bands are based on the original validation study’s population quartiles — see the table below — but BRI is newer than BMI and its interpretation is still an active area of research.
Is BRI better than BMI?: BRI directly incorporates waist circumference, so it captures fat distribution that BMI misses entirely. Whether it out-predicts other waist-based measures like waist-to-height ratio for a given health outcome is still being studied — it is one more tool in the picture, not a replacement for all others.
Why doesn’t BRI need my weight?: BRI models the body as an ellipse using only waist circumference and height, so weight isn’t a required input. This makes it usable even when weight isn’t known or trusted, though it also means it cannot capture information that weight alone would add.