Body Roundness Index (BRI) Calculator
Estimate your Body Roundness Index from waist circumference and height — a shape-based measure of central body fat that BMI misses.
How it works
BRI = 364.2 − 365.5 × √(1 − ((waist ÷ 2π)² ÷ (0.5 × height)²)), waist and height in the same units
The Body Roundness Index models your torso as an ellipse and uses waist circumference and height to estimate how "round" you are, which stands in for how much fat is packed around your middle. That central, visceral fat carries more health risk than fat elsewhere, and BMI — which only knows your total weight — cannot detect it. BRI captures body shape instead of just mass, so two people with an identical BMI can have very different BRIs if one carries more weight at the waist. Typical values run from around 1 for very lean builds to well above 6 for high central adiposity.
Worked example
With a waist of 85 cm and height of 175 cm: waist ÷ 2π = 13.53, squared = 183.0; half-height = 87.5, squared = 7,656; the ratio is 0.0239, so BRI = 364.2 − 365.5 × √(1 − 0.0239) = 364.2 − 361.3 = 2.9.
Sources: Thomas DM et al. (2013), Obesity — Body Roundness Index
Frequently asked questions
How is BRI better than BMI?
BMI uses only height and weight, so it cannot tell where fat is stored. BRI uses waist and height to estimate central (belly) fat, which is more strongly linked to metabolic and cardiovascular risk. It is a shape measure rather than a mass measure.
What is a healthy BRI?
There is no single official cutoff yet, but research generally treats lower values as leaner and healthier, with values rising as central fat increases. It is best used to track change over time and alongside other measures rather than as a strict pass/fail line.
How should I measure my waist?
Use a flexible tape around the narrowest part of your torso or at the level of the navel, snug but not compressing the skin, at the end of a normal breath out. Consistent technique matters most for tracking the number over time.
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Educational estimate, not medical advice — for clinical decisions consult a healthcare professional.