Body Roundness Index Calculator
The Body Roundness Index (BRI) models the human torso as an ellipse to quantify central adiposity (belly fat). Unlike BMI, BRI uses waist circumference and height to capture fat distribution around the abdomen, which is more closely linked to metabolic syndrome and cardiovascular disease risk. BRI ranges from approximately 1 (very lean) to 15 (very round). Enter your waist circumference and height to calculate your BRI and see your cardiometabolic risk category.
Body Roundness Index formula
BRI = 364.2 - 365.5 x sqrt(1 - ((WC / (2 x pi))^2 / (0.5 x H)^2))
Where WC is waist circumference and H is height, both in the same units (cm). The formula models the torso as an ellipse with semi-axis a = H/2 and semi-axis b = WC/(2pi). Published by Thomas et al. (2013) in PLOS ONE.
BRI interpretation (Thomas et al., 2013)
- BRI below 3.41: Very lean; estimated body fat below 20% (men) or below 30% (women)
- BRI 3.41 to 4.45: Low risk; healthy body composition range
- BRI 4.46 to 5.46: Moderate risk; increasing central adiposity
- BRI 5.47 to 6.91: High risk; elevated cardiometabolic risk
- BRI above 6.91: Very high risk; associated with body fat above 35% (men) or 40% (women)
Body Roundness Index calculator: frequently asked questions
What is the Body Roundness Index?
The Body Roundness Index (BRI) was developed by Diana Thomas and colleagues and published in 2013. It uses waist circumference (WC) and height (H) to estimate how round the body is, modelling the torso as an ellipse. BRI = 364.2 - 365.5 x sqrt(1 - ((WC / (2pi))^2 / (0.5 x H)^2)). BRI values range from approximately 1 to 15, with higher values indicating more abdominal adiposity.
Is BRI more accurate than BMI?
Research published in journals including PLOS ONE and Obesity Reviews suggests BRI may better predict visceral body fat and cardiometabolic risk than BMI. BMI does not account for fat distribution; two people with the same BMI but different waist-to-height ratios have very different cardiometabolic risk profiles. BRI captures central adiposity (belly fat), which is more strongly associated with metabolic syndrome, type 2 diabetes, and cardiovascular disease.
What is a healthy BRI value?
BRI below 4.45 is generally associated with a lower body fat percentage (below 25% in men, below 31.8% in women) and lower cardiometabolic risk. BRI above 6.91 is associated with higher body fat (above 35% in men, above 40% in women) and elevated cardiometabolic risk. These thresholds were proposed by Thomas et al. (2013) based on NHANES data analysis.
How do I measure waist circumference correctly?
Waist circumference should be measured at the midpoint between the bottom of the lowest rib and the top of the hip bone (iliac crest), at the end of normal exhalation, with the tape horizontal and snug but not compressing the skin. The WHO and NIH recommend this method. Some US guidelines measure at the top of the hip bone. Ensure consistent measurement technique.
What are the waist circumference thresholds for metabolic risk?
According to the National Institutes of Health (NIH) and National Heart, Lung, and Blood Institute (NHLBI): men with waist circumference above 40 inches (102 cm) and women with waist circumference above 35 inches (88 cm) have substantially increased risk of metabolic complications. These thresholds apply regardless of BMI.
Official sources
- Thomas DM, et al. Relationships between body roundness with body fat and visceral adipose tissue emerging from a new geometrical model. Obesity (Silver Spring). 2013;21(11):2264-71. Available via PubMed 23519954.
- National Heart, Lung, and Blood Institute: Assessing Your Weight and Health Risk.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.