Body Roundness Index
Two measurements. A clearer view of your proportions.
Your body roundness
BRI is a geometric index, not a body-fat percentage. No single universal BRI diagnostic cutoff is applied.
The geometry behind your result
Illustration, not a body scan or a scale drawing. Waist width is enlarged for readability; the equation uses the true waist-to-height ratio.
Waist-to-height context
0.471Confirm adult reference applicability to show the bands.
Ratio calculated. Adult reference context has not been confirmed.
NICE bands apply to the separate WHtR context, not universal BRI categories.
Calculation & assumptions
BRI = 364.2 − 365.5 × √[1 − (waist ÷ (π × height))²]
Height 170 cm; waist 80 cm → BRI 2.82.
- Both measurements use the same units; no intermediate rounding.
- BRI and WHtR share the same inputs. BRI is a nonlinear transformation of WHtR, not a separate measurement of body fat.
- The equation is not mathematically limited to a 1–15 score. Results outside usual adult measurements need context.
- No universal “healthy BRI” band or individual mortality probability is inferred.
Measurement guide
Stand upright without shoes to measure height. For waist, place a non-stretch tape horizontally midway between the lowest rib and the top of the hip bone. Measure after breathing out naturally without compressing the skin. Repeat consistently at the same site.
Use this adult educational tool only within the stated input range. It is not intended for children, pregnancy, or monitoring abdominal swelling. A clinician can interpret measurements in their wider context.
Frequently asked questions
What does BRI measure?
BRI is an anthropometric research index derived from height and waist circumference. It is associated with body composition at population level; it does not directly measure visceral fat or body-fat percentage.
Is BRI a diagnosis?
No. This calculator does not diagnose obesity, metabolic disease or individual mortality risk. Published cutoffs depend on the study population and outcome.
Where should I measure my waist?
For consistency with the adult WHtR context here, measure midway between your lowest rib and the top of your hip bone after a natural breath out. Do not switch measurement sites when following changes over time.
How does this differ from BMI?
BMI uses weight and height. BRI uses waist and height. These measures describe different aspects of body size and should be interpreted with other relevant clinical information.
Sources & References
Thomas et al. · 2013
NG246 · Eligibility matters.
Associations, not individual prognosis.
References inform the calculation; no institutional endorsement. Source names identify the publications and guidance.
Two measurements. A clearer view of your proportions.