Calculate your BRI — an emerging body composition metric that estimates central adiposity using waist circumference and height.
Scale: ~1 (very lean) to 16+ (high central adiposity)
BRI is a relatively new metric and standardised risk thresholds are still being established by researchers. It should not be used as a sole indicator of health. Consult a healthcare professional for a complete assessment.
The Body Roundness Index (BRI) was developed in 2013 by Diana Thomas and colleagues at Montclair State University. It uses an eccentricity-based mathematical model that treats the human body as an ellipse, using waist circumference and height to estimate how "round" a person's body shape is.
BRI produces a score typically ranging from about 1 (very lean, elongated body shape) to 16 or higher (very round body shape with significant central adiposity). The metric was designed to correlate more closely with DEXA-measured body fat percentage than simpler ratios, though it uses the same easy-to-obtain measurements as WHtR.
The BRI formula models body shape using the concept of eccentricity from ellipse geometry:
BRI = 364.2 − 365.5 × √(1 − ((waist / 2π)² / (0.5 × height)²))
Where waist circumference and height are in the same units (metres). The formula essentially measures how much your body deviates from a perfect circle based on the relationship between waist and height.
| BRI Range | Category | Implication |
|---|---|---|
| Below 3.41 | Lean | Low central adiposity |
| 3.41 – 4.45 | Healthy | Normal body composition |
| 4.45 – 5.46 | Overweight | Elevated central fat, increased risk |
| 5.46 – 6.91 | Obese I | Significant central adiposity |
| Above 6.91 | Obese II+ | High risk — seek professional guidance |
Note: These ranges are approximate. BRI thresholds are still being refined by researchers and may vary by population.
BRI gained significant public attention following a 2024 study published in JAMA Network Open that analysed data from nearly 33,000 U.S. adults. The study found a U-shaped association between BRI and all-cause mortality — both very low and very high BRI values were associated with increased mortality risk, with the lowest risk in the middle range.
Earlier validation studies have shown that BRI correlates well with DEXA-measured body fat percentage and performs comparably to or slightly better than BMI for predicting cardiometabolic risk factors including hypertension, dyslipidaemia, and insulin resistance.
Since BRI uses the same two inputs as WHtR (waist and height), the two metrics are mathematically related. Studies comparing them generally find similar predictive power for cardiovascular and metabolic outcomes. WHtR has the advantage of simplicity — a single threshold of 0.5 — while BRI offers a more granular numerical scale.
Both BRI and WHtR outperform BMI for detecting central adiposity because they incorporate waist circumference. BMI cannot tell you where fat is stored, which is the crucial factor for metabolic risk.
BRI is a relatively new metric. While research is promising, it lacks the decades of validation across diverse populations that BMI and WHtR have accumulated. Standardised risk thresholds have not yet been adopted by major health organisations, making clinical interpretation less straightforward. The complex formula also makes it impractical to calculate without a calculator, unlike WHtR's simple division.
BRI values below about 3.4 suggest a lean body shape. Between 3.4 and 4.4 is generally healthy. Above 5.5 indicates increasing central adiposity. Standardised thresholds are still being established.
Both use waist and height, but BRI applies a more complex eccentricity formula. In practice, they show similar predictive power for health outcomes.
Research suggests BRI better predicts body fat and cardiometabolic risk because it captures abdominal fat distribution, which BMI completely ignores.
Just waist circumference and height — both measurable with a standard tape measure.