A Body Shape Index (ABSI) Calculator

ABSI is a 2012 metric developed by Nir and Jesse Krakauer at the City College of New York that adjusts the standard BMI calculation for waist circumference. BMI only uses weight and height, so it cannot tell apart a person who carries weight as belly fat from a person who carries the same weight as leg muscle. ABSI was specifically designed to be statistically independent of BMI and height in the NHANES population, which lets it capture central adiposity as a separate signal of mortality risk on top of BMI.

ABSI equals waist circumference in meters divided by (BMI raised to the 2/3 power) times the square root of height in meters: ABSI = WC / (BMI^(2/3) * height^(1/2)). The unusual exponents are not arbitrary. Krakauer chose them so that the resulting index has zero correlation with BMI and height in the reference population. Dimensionally, ABSI works out to kg^(-2/3) * m^(11/6), which is why the values are small numbers around 0.07 to 0.09.

In the 2012 NHANES analysis Krakauer published in PLOS ONE, people in the top quintile of ABSI had roughly 1.5 times the all-cause mortality of people in the bottom quintile, even after controlling for BMI, age, sex, and other risk factors. The mechanism is visceral adipose tissue. A large waist for your given weight and height signals fat stored around the organs (liver, pancreas, mesentery), which drives insulin resistance, chronic inflammation, and cardiovascular disease in ways that subcutaneous fat on the hips and thighs does not.

Stand upright with your feet shoulder-width apart and breathe out normally. Find the top of your hip bone (iliac crest) and the bottom of your lowest rib, then place a flexible tape measure horizontally around your bare abdomen at the mid-point between those two landmarks. The tape should be snug but not compress the skin. Take the reading at the end of a normal exhale. Do not measure at the belly button; in many adults that lands lower than the WHO-recommended mid-point and can shift your number by several centimeters.

ABSI is a population-level statistic, not an individual diagnosis. The mortality hazard ratios it is based on are averages across thousands of people in the NHANES cohort, so a high ABSI tells you that people with your shape tend to die earlier, not that you will. ABSI also does not account for muscle mass, bone density, ethnicity-specific body composition differences, or actual visceral fat measured by DXA or MRI. Use it as one screening signal alongside BMI, waist-to-height ratio, blood pressure, lipids, and fasting glucose, and discuss any concerning values with a physician.