The Body Roundness Index (BRI) uses your waist and height to describe how round your body is, which reflects belly fat better than BMI. Enter two measurements to see your BRI, its risk band and related measures.
Last updated:
Units
Sex
Used for the body fat estimate and waist threshold; BRI itself is the same for everyone
ft
in
cm
in
At the navel, relaxed, after breathing out
cm
At the navel, relaxed, after breathing out
Enter your values to see the result.
Advertisement
Advertisement
How to use the Body Roundness Index Calculator
Choose units: inches and feet, or centimeters.
Enter your height.
Measure your waist at the navel with a relaxed stomach after a normal breath out, and enter it.
Read your BRI and where it sits on the risk chart.
Check the table to see the waist size that would move you into the lowest-risk band.
How the Body Roundness Index works
BRI treats the body as an ellipse whose long axis is your height and whose short axis comes from your waist. The rounder the ellipse (the closer the waist radius is to half your height), the higher the score:
BRI = 364.2 − 365.5 × √(1 − (WC ÷ 2π)² ÷ (0.5 × H)²), where WC is waist circumference and H is height in the same unit.
The estimated body fat uses Relative Fat Mass (RFM = 64 − 20 × height ÷ waist, + 12 for women), a separate tape-measure equation validated against DXA scans. It is shown as a rough guide, not a measurement.
BRI risk bands
BRI
Group in the 2024 NHANES study
All-cause mortality compared with the middle group
Under 3.41
Lowest fifth
Higher
3.41–4.44
Second fifth
Slightly higher
4.45–5.45
Middle fifth
Lowest (reference)
5.46–6.90
Fourth fifth
Higher
6.91 and above
Highest fifth
Highest (about 1.5 times)
Bands are from Zhang et al., JAMA Network Open (2024), which followed US adults from 1999 to 2019. They describe population risk, not an individual diagnosis, and were based on adults; they may not apply to children, pregnant women or very muscular people.
Tips for lowering your BRI
BRI changes only with your waist, so track your waist measurement monthly at the same spot and time of day.
Regular aerobic activity and strength training both reduce abdominal and visceral fat, even before the scale moves much.
Eating more fiber and protein and fewer sugary drinks and refined carbs tends to reduce belly fat over time.
Sleep and stress matter: short sleep is linked with more abdominal fat.
A very low BRI can also matter; if you are losing weight without trying, talk to a doctor.
Frequently asked questions
What is the Body Roundness Index?
The Body Roundness Index is a body shape measure introduced by Diana Thomas and colleagues in 2013. It models the body as an ellipse using waist circumference and height, so it captures abdominal fat better than BMI, which uses only weight and height. Scores usually range from about 1 to 20.
How is BRI calculated?
BRI = 364.2 − 365.5 × √(1 − (waist ÷ 2π)² ÷ (0.5 × height)²). Waist and height must be in the same unit. For example, a 34-inch waist at 65 inches tall gives a BRI of about 3.8.
What is a good BRI score?
In a 2024 study of about 33,000 US adults (NHANES), people with a BRI between about 4.45 and 5.45 had the lowest risk of death from any cause. Risk was higher at both ends: below 3.41 and especially at 6.91 or more. There is no official clinical cut-off yet.
Is BRI better than BMI?
BRI reflects where fat is stored, especially around the waist, which is more closely linked to heart disease and diabetes than total weight. BMI cannot tell muscle from fat. Many researchers see BRI as a useful addition to BMI rather than a full replacement.
Can the calculator measure my visceral fat?
Not directly. Visceral fat can only be measured with scans such as DXA, CT or MRI. The calculator flags a visceral fat risk using well-known waist thresholds (102 cm or 40 in for men, 88 cm or 35 in for women) and the waist-to-height ratio of 0.5.
How do I measure my waist correctly?
Stand upright, breathe out normally and wrap a flexible tape measure around your bare stomach at the level of the navel, keeping it snug but not compressing the skin and parallel to the floor. Take two measurements and use the average.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.