BRI Frequently Asked Questions
What is the Body Roundness Index (BRI)?
The Body Roundness Index is a body-shape index introduced by Thomas and colleagues in 2013. It models the human body as a vertical ellipse and quantifies “roundness” from waist circumference and height only — no weight needed. Scores typically fall between 1 and 16, and rounder individuals get higher values. It was designed as a geometric proxy related to body fat and visceral adipose tissue.
What is the BRI formula?
BRI = 364.2 − 365.5 × √(1 − ((waist/(2π))² / (0.5×height)²)), with waist and height in the same unit. Worked example: waist 72 cm, height 160 cm → waist-to-height ratio 0.450, ellipse eccentricity 0.98969, BRI = 364.2 − 365.5×0.98969 = 2.47. This calculator evaluates the same formula in cm or inches.
What is a good BRI score?
There are no universally agreed clinical cut-offs, so bands are descriptive: below 1 very lean, 1–2.99 lean, 3–3.99 average roundness, 4–5.99 above-average roundness, 6–11.99 high roundness, 12 and above very high roundness. The original paper described lean bodies below 3 and severely obese bodies above 12, with overlap between adjacent bands. Treat any band as an educational description, not a diagnosis.
Is BRI better than BMI?
They measure different things. BMI sees only weight and height, so it cannot tell belly fat from muscle — a muscular athlete can score “overweight”. BRI sees shape: waist relative to height, which tracks central roundness and, by geometry, visceral-fat tendency. Research on which predicts outcomes better is mixed, so the educational reading is to use them together: BMI for weight status, BRI for shape.
Does BRI predict visceral fat?
In the original 2013 study, BRI predicted percentage body fat and visceral adipose tissue volume in the study samples, which is why it is described as a visceral-fat proxy rather than a scale reading. Reported population means were about 4.64 for men and 5.16 for women. Later studies continued investigating links with cardiometabolic markers, but results vary — BRI remains a research index, not a diagnostic test.
What waist circumference gives a BRI of 3.5?
It depends on height, because the formula is solved backwards: waist = π × height × √(1 − e²) with e = (364.2 − BRI)/365.5. For a height of 175 cm and a target BRI of 3.5, the waist is 88.8 cm (about 35.0 in). Use the Target Waist Solver tab above for any height and any target between 1 and 16.
How do I measure my waist correctly for BRI?
Stand relaxed and find the midpoint between your lowest rib and the top of your hip bone (iliac crest). Wrap a tape measure horizontally around that point, snug but not compressing the skin, and read at the end of a normal relaxed exhale. Measure twice and average. Note that tape measurements vary more in standing obese individuals, which adds noise to any waist-based index.
Can I calculate BRI in inches?
Yes. Waist and height only need the same unit because the units cancel inside the formula. Example: waist 28.35 in and height 62.99 in give BRI 2.47 — identical to 72 cm / 160 cm. Toggle the cm/inches switch on the calculator tab and the result is the same.
Why isn’t body weight in the BRI formula?
By design. BRI is a pure shape index: it compares your waist circle (unrolled to a radius, waist/2π) against half your height as the two axes of an ellipse. Weight would turn it into another mass index like BMI. That is exactly the point of the 2013 paper — to capture roundness independently of how heavy you are.
Is BRI a medical diagnosis?
No. BRI is an educational research index, not a medical device and not a diagnosis. It does not account for ethnicity, family history, diet, physical activity, or organ health, and no single number can assess your health. Use it as a shape estimate for learning, and discuss any health concern with a qualified health professional.
What is the difference between BRI and ABSI?
Both are waist-based research indices but with different formulas and aims. ABSI (Krakauer & Krakauer 2012) is waist divided by (BMI^(⅔) × height^(½)) and was studied mainly for mortality risk. BRI (Thomas et al. 2013) is 364.2 − 365.5 × eccentricity of the body ellipse and was designed as a roundness and visceral-fat proxy. Our ABSI calculator covers the other index.
What are the limitations of BRI?
Four to know: (1) waist tape measurements are noisy, especially in standing obese people; (2) the index ignores ethnicity, family history, diet, activity, and organ health; (3) there are no universal clinical cut-offs, so bands are descriptive and overlap; (4) it is validated as a research index, not as a diagnostic tool. Treat BRI as one educational data point, never a verdict.
Method & sources
The body roundness index was introduced by Thomas, Bredlau, Bosy-Westphal and colleagues in Obesity (2013), “Relationships between body roundness with body fat and visceral adipose tissue emerging from a new geometrical model”. The paper models the body as an ellipse and reports that BRI predicted percentage body fat and visceral adipose tissue in its study samples; reported population means were about 4.64 for men and 5.16 for women.
All computation on this page runs locally in your browser — no measurements leave your device.
Health disclaimer: BRI is an educational research index, not a medical device and not a diagnosis. It does not account for ethnicity, family history, diet, activity, or organ health. If you have health concerns, discuss them with a qualified health professional.