BRI Calculator: Body Roundness Index
Calculate body roundness index and waist-to-height ratio from centimeters or inches, with the formula and its limits explained.
Your inputs
Choose the units and assumptions that match your data. Example inputs are illustrative.
Your result
Enter your values, then choose Calculate.
Results are calculated in your browser. Display rounding does not change the underlying calculation.
Calculation breakdown
Method, assumptions and worked example
How it works
BRI = 364.2 − 365.5 × √[1 − (waist ÷ (π × height))²]. Waist and height must use the same unit, so the index is unitless. The tool also displays waist ÷ height as a separate ratio.
Worked example
For height 175 cm and waist 85 cm, waist-to-height ratio is 0.486 and BRI is about 3.09.
Using the result
Use a consistent waist measurement site and technique. Research associations at population level do not give an individual diagnosis. This page intentionally assigns no universal BRI health bands or life-expectancy prediction. Results below zero or outside the formula domain are rejected instead of labeled healthy.
Frequently asked questions
Does BRI use weight?
No. It uses waist circumference and height.
Can BRI diagnose disease?
No. It is a body-shape index; clinical interpretation needs other information.
Method review and references
Formula and content reviewed on 10 October 2026. Worked examples are hypothetical. Methods and assumptions are explained on each page. Health estimates are not clinical measurements; symbolic tools are for entertainment.