Body Roundness Index Calculator

How it is calculated

The tool models the body as an ellipse. Waist and height are entered in centimetres and converted to metres. It then computes r = (waist / 2π)² / (0.5 × height)², the eccentricity e = √(1 − r), and finally BRI = 364.2 − 365.5 × e. A rounder midsection gives a lower eccentricity and therefore a higher BRI. The category rule in this tool is: below 3.41 is Low, 3.41 to 6.9 is Normal, and above 6.9 is High. If the waist is so large relative to height that r reaches 1 (waist of about π times height), no result is shown. Weight, age and sex are not used, and the category cut-offs are the tool's own simple bands rather than a diagnosis.

Common mistakes

• Entering inches or metres. Both fields are in centimetres, so a 1.75 height or a waist of 37 inches gives a meaningless result.
• Measuring the waist over clothing or at the hips. It should be taken around the natural waist, level with the navel, otherwise the index is shifted.
• Comparing the number with a BMI scale. BRI uses its own scale, and values around 3 to 7 are typical of this tool's bands, not BMI-like numbers.
• Reading the category as a medical verdict. It is only a rough band on a body-shape index; weight, muscle and age are not considered.
• Using it for children or during pregnancy. The tool applies the same adult-style formula and bands to everyone, so the category is not meaningful in those cases.