Body Mass Index tells you how heavy you are for your height, but it cannot tell where that weight lives. Two people with the same BMI can carry fat very differently: one around the hips and thighs, the other packed around the organs in the abdomen. That second pattern — often called central or abdominal obesity — carries a markedly higher risk of heart disease, type 2 diabetes, and premature death, even when the BMI looks perfectly ordinary.
The Body Shape Index, better known by its acronym ABSI (A Body Shape Index), was developed by doctors Dawne and Nir Krakauer and published in PLOS ONE in 2012 to measure exactly this. By taking your waist circumference and adjusting it for both your BMI and your height, ABSI captures the abdominal-fat burden that BMI alone misses. This calculator lets you enter the BMI you already know — from a smart scale, a medical visit, or a prior BMI check — and instantly shows your ABSI score, where you sit on the adult distribution, and your estimated relative mortality risk.
How to Use
- Measure your Waist Circumference at the level of your navel, standing relaxed after exhaling. Keep the tape snug but not squeezing the skin. Most people underestimate this number, so pull the tape out and check it twice.
- Enter your Height without shoes. The ABSI formula needs height in meters, so the engine converts centimeters for you automatically.
- Type the BMI you already know. This is the key difference from a generic weight-and-height tool: if your scale, doctor, or another calculator already gave you a BMI, you can reuse it here instead of re-entering weight.
- Add your Age and choose your Sex. ABSI reference norms are adult age-adjusted values; mortality hazards differ modestly between male and female reference groups.
- Read the result card. The highlighted ABSI number is your body-shape score, the Z-score tells you how far above or below average you are, and the Risk Category plus Relative Mortality Risk translate that score into a plain-language comparison against an average adult of the same reference group.
A typical adult scores near 0.08. Lower is better; a rising waist at a fixed BMI pushes ABSI up and signals more visceral fat.
The Body Shape Index Formula
ABSI is a dimensionless ratio built to be independent of height and BMI on average, so that people of very different sizes can be compared on the same scale:
ABSI = Waist (m) ÷ ( BMI^(2/3) × Height (m)^(1/2) )
Where waist and height are in meters and BMI is in kg/m². The exponent on BMI (2/3) and the square root of height are chosen so that, across a large reference population, ABSI correlates only weakly with BMI and height — leaving it to describe body shape, not body size.
On the default inputs — waist 90 cm, height 173 cm, BMI 25 — the engine converts waist to 0.90 m and height to 1.73 m, then computes: denominator = 25^(2/3) × √1.73 ≈ 11.25, and ABSI = 0.90 ÷ 11.25 ≈ 0.080. That lands almost exactly on the adult reference mean of 0.082, which is why a BMI-25 adult with a 90 cm waist sits right in the "Average" band.
Your Z-score is then (ABSI − 0.082) ÷ 0.009, where 0.009 is the reference standard deviation. A Z-score of +1 means you are one standard deviation above the average adult's abdominal burden. The engine converts that into a Relative Mortality Risk of exp(0.35 × Z-score), the hazard ratio the Krakauers reported for all-cause mortality.
How to Read Your Risk Category
The Z-score bands are deliberately simple:
- Low (Z below −0.5) — below-average abdominal adiposity; roughly a 83% relative mortality risk versus the average adult.
- Average (Z from −0.5 to +0.5) — in the central band of the population.
- Higher (Z from +0.5 to +1.5) — noticeably central, worth discussing with a clinician.
- Highest (Z above +1.5) — well above average visceral fat; the relative mortality risk climbs to roughly 170% or more.
The waist-to-height ratio shown alongside is a quick sanity check: keeping it under about 50% is the widely cited rule of thumb, and ABSI refines that rule by accounting for BMI and height more precisely.
Examples
Example 1 — The default adult. Waist 90 cm, height 173 cm, BMI 25, age 40, male. ABSI comes out at about 0.080, the Z-score near −0.22, the risk category Average, and the relative mortality risk about 0.93 — essentially in line with an average adult. The waist-to-height ratio is 52.0%, just over the 50% guideline, which is consistent with an "Average" rather than "Low" reading.
Example 2 — A slim but centrally shaped person. Waist 80 cm, height 165 cm, BMI 22, age 35, female. ABSI is roughly 0.079, still in the Average band with a relative mortality risk around 0.90%. Notice that a "normal" BMI of 22 does not by itself guarantee a low ABSI; the waist-to-height ratio here is 48.5%, comfortably under 50%.
Example 3 — High visceral fat at a normal BMI. A 40-year-old man with a BMI of only 24 but a waist of 105 cm pushes ABSI above 0.10, a Z-score over +2. The risk category flips to Highest and the relative mortality risk rises past 200% of average — the classic "normal-weight obese" pattern that BMI alone completely misses. This is the scenario ABSI was designed to expose.
FAQ
What is a good Body Shape Index (ABSI) value?
In the adult reference population the mean ABSI is about 0.082 with a standard deviation of about 0.009. Scores near or below 0.08 are average to low; a score around 0.09 or higher (a Z-score above +0.5) puts you in the "Higher" band, and 0.10+ (Z-score above +1.5) is the "Highest" band. Lower is generally better for long-term mortality risk.
How is ABSI different from BMI?
BMI compares your total weight to your height squared and cannot tell where the weight is stored. ABSI adjusts your waist circumference for both BMI and height, so it specifically quantifies abdominal (visceral) fat. Two people can share a BMI of 25 but have very different ABSI scores depending on their waist size, and that difference predicts mortality better than BMI alone in large population studies.
Do I need to enter my weight?
No. This calculator is built for people who already know their BMI — from a smart scale, a doctor's visit, or another BMI tool. You enter waist, height, and that known BMI directly. If you do not know your BMI yet, compute it first with a standard BMI calculator and then come back here with the number.
What does the Z-score mean?
The Z-score says how many standard deviations your ABSI sits from the adult reference mean of 0.082. A Z-score of 0 is exactly average; +1 is one standard deviation above average (roughly the "Higher" band); −1 is one standard deviation below (roughly "Low"). The engine then turns the Z-score into a relative mortality risk using exp(0.35 × Z).
How do I measure my waist correctly?
Stand relaxed, find the top of your hip bone and the bottom of your ribs, and place the tape midway between them — roughly at the navel. Breathe out normally and measure without pulling the tape tight into your skin. Take two readings and average them. Measuring over clothing or sucking in your stomach will underestimate the true waist and underestimate your ABSI.
Is ABSI a diagnosis?
No. ABSI is a population-level research metric that stratifies risk, not a diagnostic test. It cannot by itself confirm disease, and it does not replace waist-to-height ratios, blood pressure, lipid panels, or a clinical exam. Use the result as a conversation starter with your doctor, especially if you land in the "Higher" or "Highest" band.
Disclaimer
This body shape index (ABSI) calculator is provided for informational purposes only and is not medical advice. The ABSI formula and reference norms come from Krakauer & Krakauer (2012) and describe population-level associations, not individual health outcomes. Relative mortality risk is a statistical estimate, not a prediction for any one person. Always discuss your results, your waist size, and any concerns with a qualified healthcare professional before making changes to diet, exercise, or medication.