BAI (Body Adiposity Index) Calculator
Calculate your Body Adiposity Index from hip circumference and height. Estimates body fat percentage without a scale, with sex-specific categories and comparison to BMI.
Body Roundness Index (BRI) Calculator
Calculate the Body Roundness Index from waist circumference and height. Compares BRI to BMI, WHtR, and ABSI with cardiometabolic risk categories and waist circumference thresholds.
โ ๏ธ Note: BRI is a research index for body shape assessment, not a clinical diagnostic tool. It supplements โ but does not replace โ BMI, waist circumference, and clinical evaluation. Body composition is best assessed with DXA or hydrostatic weighing.
e.g. 175
cm
At navel level
cm
For BMI/ABSI comparison
kg
Planning notes, formulas, and examples
About the Body Roundness Index (BRI) Calculator
The Body Roundness Index (BRI) is a body shape metric developed from an ellipse-based body model that uses waist circumference and height to compute an eccentricity-based index. Unlike BMI, which only considers weight and height, BRI directly incorporates waist circumference โ a strong proxy for visceral adiposity and cardiometabolic risk.
BRI values typically range from 1 (very lean) to 15+ (severely obese). Research has shown BRI to be a stronger predictor of metabolic syndrome, type 2 diabetes, and cardiovascular disease than BMI alone, particularly in populations where BMI fails to distinguish lean muscle mass from fat mass. The ellipse model assigns higher BRI values to "rounder" body profiles โ those with greater central adiposity relative to height.
This calculator computes BRI alongside multiple body composition indices (BMI, WHtR, ABSI), estimates body fat percentage from BRI, and provides comprehensive reference tables for waist circumference risk thresholds across populations.
When This Page Helps
BRI captures central adiposity better than BMI because it directly includes waist circumference. This calculator is useful when you want body-shape context alongside BMI, WHtR, and ABSI so the risk picture is not reduced to weight alone.
How to Use the Inputs
- Select metric (cm/kg) or imperial (in/lb) units.
- Enter your height and waist circumference (measured at navel level, standing, after exhale).
- Optionally enter weight for BMI and ABSI comparison.
- Review BRI score, category, and comparison to other body composition indices.
- Check waist circumference against population-specific risk thresholds.
Formula used
BRI = 364.2 โ 365.5 ร โ(1 โ ((WC / 2ฯ)ยฒ / (0.5 ร H)ยฒ))
Where:
- WC = waist circumference (cm)
- H = height (cm)
- Body eccentricity e = โ(1 โ (WC/2ฯ)ยฒ / (0.5รH)ยฒ)
Additional indices:
- WHtR = WC / H
- BMI = weight (kg) / height (m)ยฒ
- ABSI = WC / (BMI^(2/3) ร H^(1/2))Example Calculation
Result: BRI: 4.12 โ Healthy range.
With a height of 175 cm and waist circumference of 88 cm, the BRI is 4.12, placing this individual in the healthy category (3.41-4.45). The waist-to-height ratio of 0.503 is just above the 0.5 threshold โ suggesting borderline central adiposity risk.
Tips & Best Practices
- Measure waist circumference at the same time of day (preferably morning) for consistency.
- A WHtR < 0.5 is a simple and powerful health target for all adults.
- BRI is most useful for people whose BMI may be misleading โ athletes, elderly, and certain ethnic groups.
- Track BRI over time alongside weight to see if body shape is changing independently of mass.
- Combine BRI with blood pressure, fasting glucose, and lipid levels for a comprehensive metabolic risk profile.
The Ellipse Model of Body Shape
Thomas et al. proposed modeling the human trunk as an ellipse, where height defines the major axis and waist circumference defines the cross-section. The eccentricity of this ellipse โ how "round" vs. "elongated" the body is โ forms the mathematical basis of BRI. A perfectly cylindrical body (eccentricity = 0) would have the maximum BRI, while a very elongated body (eccentricity โ 1) would approach BRI = 1.
BRI and Cardiometabolic Risk
Multiple large cohort studies have validated BRI as a predictor of cardiometabolic outcomes. A meta-analysis of 15 studies found BRI to have a stronger association with metabolic syndrome than BMI (pooled AUC 0.69 vs 0.65). BRI has been particularly useful in East Asian populations, where metabolic risk occurs at lower BMI values but is well-captured by waist-centric indices.
Limitations and Future Directions
BRI's main limitations are: (1) it cannot distinguish visceral from subcutaneous fat, (2) it does not account for muscle mass, and (3) population-specific cutoff values are still being established. Future work combining BRI with bioelectrical impedance analysis (BIA) or CT-derived visceral fat area may improve its clinical utility as a non-invasive risk stratification tool.
Sources & Methodology
Last updated:
Methodology
This calculator applies the published Body Roundness Index equation to waist circumference and height, then adds comparison values such as waist-to-height ratio, BMI, and ABSI when the needed inputs are provided. The purpose is to show how a waist-based body-shape index behaves alongside more familiar screening measures.
BRI is a risk-context tool rather than a diagnosis. It is useful because it emphasizes central adiposity, but the result should still be interpreted alongside actual cardiometabolic measurements such as blood pressure, glucose, lipids, and overall clinical context.
Sources
- Relationships between body roundness with body fat and visceral adipose tissue emerging from a new geometrical model (PubMed / Obesity) โ Original Body Roundness Index publication by Thomas et al.
- Waist-to-height ratio as an indicator of โโearly health riskโโ (PubMed / International Journal of Food Sciences and Nutrition) โ Reference background for the waist-to-height-ratio comparison used on the page.
Frequently Asked Questions
BRI better captures central adiposity because it includes waist circumference. Research shows BRI is a stronger predictor of metabolic syndrome and cardiovascular disease than BMI in many populations. However, BMI has far more epidemiological data and remains the standard in clinical guidelines. BRI is best used as a complement to BMI.
Measure waist circumference at the midpoint between the lowest rib and the iliac crest (approximately navel level) while standing, after a normal exhale, with a non-elastic tape measure snug against the skin. Do not compress the skin. Take 2-3 measurements and average them.
A WHtR below 0.5 is associated with low cardiometabolic risk across all ages and ethnicities. Above 0.5 indicates increased risk. This simple threshold ("keep your waist less than half your height") is one of the most universal health markers available.
No. Like BMI, BRI cannot distinguish between fat and lean tissue. Athletic individuals with large abdominal circumference due to muscle development may get misleadingly high BRI values. Body fat percentage measurement (DXA, BIA) is needed for definitive composition assessment.
BRI values of 3.41-4.45 are generally associated with the lowest all-cause mortality and cardiometabolic risk in population studies. However, optimal ranges may vary by age, sex, and ethnicity. BRI thresholds are still being refined through ongoing research.
A Body Shape Index (ABSI) measures the excess waist circumference beyond what would be predicted by BMI and height alone. Higher ABSI indicates more central adiposity independent of overall body size. It is a useful complement to BRI for mortality risk assessment.
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