Comprehensive Calculator Guide
The body roundness index (BRI) describes your shape — closer to lean and long, or round around the middle — from just your height and waist. At 175 cm with an 85 cm waist BRI is 3.09; at 170 cm with a 100 cm waist it is 5.16. The calculator places your result on the ranges a large study linked to mortality risk, with your waist-to-height ratio alongside.
The idea and the evidence
Diana Thomas and colleagues proposed BRI in 2013, modelling the body as an ellipse whose length is your height and whose width comes from your waist. The rounder the shape, the higher the index.
A 2024 JAMA Network Open study analysed about 33,000 US adults surveyed between 1999 and 2018. Risk of death was lowest in the middle group (about 4.5–5.5) and higher at both ends: about 25% higher under 3.4 and about 49% higher at 6.9 or above. It’s a population-level association, not a personal diagnosis.
How to Use
- Enter your height.
- Enter your waist in the same unit, measured at the navel.
- Press “Calculate BRI” to see your index, where it sits and your waist-to-height ratio.
Formula Used
BRI = 364.2 − 365.5 × √(1 − (waist ÷ 2π)² ÷ (0.5 × height)²)
Practical Examples
- Example 1
- 175 cm and an 85 cm waist: BRI 3.09, waist-to-height 0.49.
- Example 2
- 170 cm and a 100 cm waist: BRI 5.16, waist-to-height 0.59.
Important Tips
- Use it alongside BMI; each shows something the other misses.
Common Mistakes to Avoid
- Measuring over clothes or at the belt line instead of the navel.
Frequently Asked Questions
- What is the body roundness index?
- A measure of body shape from height and waist that reflects belly fat.
- What is a healthy BRI?
- In the 2024 study, risk was lowest at about 4.5–5.5 and higher below 3.4 or above 6.9.
- How is it different from BMI?
- BMI uses weight and can’t tell muscle from fat; BRI uses the waist, so it focuses on belly fat.