# Body Roundness Index Calculator (BRI)

URL: https://speedycalculator.com/calculators/health/body-roundness-index/
Last updated: 2026-10-30

> The body roundness index calculator estimates how round your body is from your waist circumference and height. BRI predicts body fat and visceral fat better than BMI, and large studies link both very low and high BRI values with higher mortality.

## Inputs

- Waist circumference (cm, in, m, ft, mm)
- Height (cm, in, m, ft, mm)

## Results

- Body roundness index
- Mortality risk vs the lowest-risk group

## Formula

```
BRI = 364.2 − 365.5 × √(1 − ((waist ÷ 2π)² ÷ (0.5 × height)²))
```

## Explanation

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)

BRIRisk compared with BRI 4.45–5.46below 3.41About 25% higher3.41–4.45Similar4.45–5.46Lowest (reference)5.46–6.91About 25% higherabove 6.91About 49% higher

### Inputs explained

FieldWhat to enterWaist circumferenceUnits: cm, in, m, ft, mmHeightUnits: 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.*

## 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.

## FAQ

**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.


## Sources

- [Thomas DM et al. Relationships between body roundness with body fat and visceral adipose tissue. Obesity, 2013](https://pubmed.ncbi.nlm.nih.gov/23519954/)
- [Zhang X et al. Body roundness index and all-cause mortality among US adults. JAMA Netw Open, 2024](https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2819971)