Body Roundness Index (BRI) Calculator
Estimate body roundness index from waist circumference and height — a body-shape measure that tracks visceral fat better than BMI alone.
How it works
BRI = 364.2 − 365.5 × √(1 − ((WC ÷ 2π) ÷ (0.5 × height))²) · WC and height in metres
The body roundness index models the body as an ellipse and derives its eccentricity from waist circumference and height, producing a single number — typically between about 1 and 16 — that captures how round versus lean a person is. Because it is built on waist size, BRI reflects central and visceral fat, which drives cardiometabolic risk more directly than the weight-and-height BMI. Recent large cohort studies have linked both very low and very high BRI to higher mortality, making it a useful complement to BMI rather than a replacement.
Worked example
For a waist of 85 cm (0.85 m) and height 175 cm (1.75 m): WC ÷ 2π = 0.135, divided by 0.5 × 1.75 = 0.875 gives a ratio of 0.155. BRI = 364.2 − 365.5 × √(1 − 0.155²) = 364.2 − 361.1 ≈ 3.1.
Sources: Body roundness index
Frequently asked questions
How is BRI different from BMI?
BMI uses weight and height and cannot distinguish fat from muscle or say where fat sits. BRI uses waist circumference and height, so it captures body shape and central fat — a stronger signal for metabolic risk in many studies.
What is a healthy BRI?
There is no single official cut-off, but research often places the lowest risk in a middle band (roughly 3.4–5.5) and higher risk at both extremes. Interpret it alongside other measures rather than in isolation.
How do I measure my waist correctly?
Measure around the narrowest point between the lowest rib and the top of the hip bone, at the end of a normal breath, with the tape snug but not compressing the skin.
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Educational estimate using standard published formulas — not medical advice, a diagnosis, or a substitute for clinical judgement. Dosing, diagnosis and treatment must be decided by a qualified clinician using validated tools and the full clinical picture.