Body composition calculator
ABSI calculator
A Body Shape Index — the part of your waist size that BMI cannot see, scored against the population you belong to. Free, instant, no sign-up.
Waist is the most movable number on this page — the coach builds the plan that shifts it.
What is A Body Shape Index?
ABSI was published by Nir and Jesse Krakauer in PLoS ONE in 2012. They started from a simple observation: waist circumference predicts death better than BMI does, but a large part of any waist measurement is just the consequence of being a large person. So they worked out how big a waist you would expect from someone's height and weight, and defined ABSI as the ratio of the actual waist to that expectation. What is left is body shape with body size divided out — and in their cohort of 14,105 US adults it predicted mortality hazard on top of BMI, not instead of it.
How this calculator works
ABSI = waist ÷ (BMI^⅔ × height^½). Your index is then turned into a z-score against the mean and standard deviation for your age and sex from NHANES 1999-2004, the reference table published with the original paper, and the z-score is read against the quintile boundaries the authors used: below −0.868 is very low risk, above +0.798 is very high. Between the bottom and top fifths they observed roughly a 1.6-fold difference in death rate over the follow-up period.
Why the units matter here
ABSI is not dimensionless. Its units are m^(11/6)·kg^(−2/3), which means the published index — and every reference value derived from it — only makes sense with waist and height in metres and weight in kilograms. Enter the same waist in centimetres and you get a number about 3.2 times larger, which will still look plausible and will be completely wrong against the reference table. This calculator converts whatever you type into SI before the equation sees it, so a typical adult result lands near 0.08. If you see an ABSI in the low hundreds somewhere else, that calculator is using centimetres.
How to use the number
A high ABSI means your waist is large for your height and weight — central fat rather than fat in general — which is the pattern most consistently tied to metabolic risk. The bands are population quintiles, not clinical thresholds: landing in "very high" is a reason to pay attention to waist circumference, not a diagnosis. Measure at the navel, relaxed, at the end of a normal breath out, and compare the number against your own previous readings rather than against anyone else's.