BRI Calculator — Body Roundness Index
Calculate Body Roundness Index (BRI) from waist circumference and height, with step-by-step math and official (government) measuring guidance updated for 2026.
⚠️ Educational tool, not medical advice. BRI is a research-derived metric; many health systems publish stronger public guidance for waist and waist-to-height ratio than for “BRI cutoffs.”
Enter measurements
Use metric or imperial — the calculator converts and keeps units consistent.
Advanced (optional): add weight to show BMI alongside BRI
BMI is widely used; BRI focuses more on midsection size relative to height.
How to measure (official government guidance)
Accurate waist measurements matter. These are government resources (current guidance pages are reviewed on multi-year cycles; we reference the latest versions available as of 2026).
- NHS (UK): how to measure your waist
- Australian Government: AUSDRISK waist measurement instructions
- CDC (US): waist measuring tip (healthy weight guidance)
- NIH/NLM (US): detailed waist circumference measuring instructions
- Australian Government: BMI and waist measurement overview
- NHS: waist-to-height ratio calculator (same inputs as BRI)
BRI formula (math-rendered)
BRI is computed from waist and height via an ellipse-based “eccentricity” model (research hosted by NIH/PMC). Source: NIH/PMC (Thomas et al.)
What does BRI mean (practical interpretation)
In general, a higher BRI indicates a rounder midsection relative to height. Unlike BMI, BRI ignores weight and focuses on central body size. There is no single global “healthy BRI cutoff” published across governments, so treat this as a screening-style metric and rely on official waist/WHtR guidance and clinical context.
- Lower BRI → typically leaner midsection for your height.
- Higher BRI → typically more central size for your height.
- Best companion metric: Waist-to-height ratio (WHtR). NHS messaging commonly simplifies this as “keep your waist to less than half your height.”
Internal links (recommended): BMI Calculator • Waist-to-Height Ratio • Health Tools