A body-shape measure based on waist and height
Updated October 2026
Stand relaxed with feet together, breathe out normally, and wrap the tape around the waist at the navel, level all the way around and snug without pressing into the skin. Studies use slightly different landmarks (the navel or the top of the hip bones), so pick one and use it every time you remeasure. Measure height without shoes against a wall. Enter both in the same unit: centimeters or inches. The result shows your BRI, which of the five groups from the 2024 mortality study it falls in, your waist-to-height ratio, and the U.S. adult average for comparison.
BRI = 364.2 − 365.5 × √(1 − (waist ÷ 2π)² ÷ (½ × height)²). The waist divided by 2π is the radius of a circle with that circumference; half the height is the long radius of the body modeled as an ellipse. For someone 175 cm tall with a 90 cm waist: 90 ÷ 2π = 14.324 cm; half the height is 87.5 cm; (14.324 ÷ 87.5)² = 0.0268; √(1 − 0.0268) = 0.9865; 364.2 − 365.5 × 0.9865 = 3.63. The square root is the ellipse’s eccentricity: the rounder the shape, the smaller it gets and the higher the BRI.
BRI was introduced in 2013 by researchers who modeled the body as an ellipse: the waist sets its width, height its length, and the index captures how round rather than how heavy the shape is. Because it uses waist size, it tracks abdominal and visceral fat better than body mass index, which cannot tell muscle from fat or where fat sits. In the original study, BRI predicted body fat percentage and visceral fat (measured by DXA and MRI) slightly better than BMI or waist size alone.
| Waist | BRI at 165 cm (5’5”) | BRI at 180 cm (5’11”) |
|---|---|---|
| 75 cm (29.5 in) | 2.55 | 1.93 |
| 85 cm (33.5 in) | 3.65 | 2.85 |
| 95 cm (37.4 in) | 4.89 | 3.89 |
| 105 cm (41.3 in) | 6.28 | 5.06 |
| 115 cm (45.3 in) | 7.81 | 6.34 |
At the same waist, a taller person has a lower BRI, so two people with a 95 cm waist can land in different study groups.
A 2024 study in JAMA Network Open followed 32,995 adults from the National Health and Nutrition Examination Survey (NHANES) for a median of about 10 years. Average BRI rose from 4.80 in 1999-2000 to 5.62 in 2017-2018. Risk of death from any cause followed a U shape:
| BRI group | All-cause mortality vs the middle group (fully adjusted) |
|---|---|
| Below 3.4 | 25% higher (hazard ratio 1.25) |
| 3.4 to 4.5 | Between the lowest and middle groups |
| 4.5 to 5.5 | Reference group |
| 5.5 to 6.9 | Between the middle and highest groups |
| 6.9 or higher | 49% higher (hazard ratio 1.49) |
The authors call BRI a promising screening tool that still needs validation in other groups; no health agency has adopted BRI cutoffs. The closest official guideline is the waist-to-height ratio in the UK’s NICE obesity guideline (recommendations from 2022): 0.4 to 0.49 is healthy central adiposity, 0.5 to 0.59 increased, and 0.6 or more high, for adults with a BMI under 35.
Treating a low BRI as a warning for a lean, active person. The higher risk below 3.4 in the study likely reflects illness or frailty in some people, not leanness itself. Comparing readings taken at different landmarks or after a meal. A 2 cm difference in waist changes BRI by about 0.2 to 0.3 at common sizes. Mixing units, such as height in inches and waist in centimeters, produces a meaningless number. Reading the hazard ratios as personal odds. They describe groups of people after statistical adjustment, not what will happen to one person. Using it in pregnancy or for children: the study covered non-pregnant adults 20 and older.
BRI is a screening number, not a diagnosis. It does not measure blood pressure, blood sugar, cholesterol, fitness or family history, which together describe health risk far better than any body-shape index. If your BRI is in the highest group or your waist-to-height ratio is 0.6 or above, ask your doctor about a checkup that includes those measures. See a doctor promptly for unexplained weight loss, a waist that is growing quickly without a change in habits, or swelling of the abdomen.