BRI models the body as an ellipse: the rounder the ellipse, the higher the index. Values usually run from about 1 to 16. A 2024 study of US adults (NHANES) found the lowest mortality at BRI 4.5–5.5, with a U-shaped rise either side.
How to use the Body Roundness Index Calculator
- Waist circumference
- Height
Results update as you type, and every field accepts the units shown in its menu.
How it works
Measure your waist at the navel and your height. The calculator converts them to the same unit, computes the eccentricity of an ellipse with those axes and maps it onto the BRI scale.
BRI and mortality risk (NHANES 1999–2018)
| BRI | Risk compared with BRI 4.45–5.46 |
|---|---|
| below 3.41 | About 25% higher |
| 3.41–4.45 | Similar |
| 4.45–5.46 | Lowest (reference) |
| 5.46–6.91 | About 25% higher |
| above 6.91 | About 49% higher |
Inputs explained
| Field | What to enter |
|---|---|
| Waist circumference | Units: cm, in, m, ft, mm |
| Height | Units: cm, in, m, ft, mm |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
BRI = 364.2 − 365.5 × √(1 − ((waist ÷ 2π)² ÷ (0.5 × height)²))
Worked example
Inputs — Waist circumference: 90 cm; Height: 175 cm.
Results — Body roundness index = 3.63; Mortality risk vs the lowest-risk group = Average.
Key terms
- Eccentricity
- How far an ellipse is from a circle.
Frequently asked questions
What is a good BRI?
Values between about 4.5 and 5.5 were associated with the lowest risk in US adults.
Is BRI better than BMI?
It reflects waist fat, which BMI misses, and is more closely related to visceral fat.
Who developed BRI?
Diana Thomas and colleagues in 2013.