What ABSI means
BMI has a famous blind spot: it cannot tell where your mass is carried. A Body Shape Index was designed in 2012 by Nir and Jesse Krakauer to address exactly that, by expressing waist circumference relative to the size that height and weight would predict. The construction is deliberate: in their analysis of 14,105 adults from the US NHANES survey, ABSI was nearly uncorrelated with height, weight, and BMI, which means it adds genuinely independent information about shape rather than restating size. Their key population-level finding was that mortality hazard rose with above-average ABSI, independently of BMI. A higher ABSI simply means your waist is larger than expected for your height and mass compared with the reference population; a lower one means the opposite. That is the entire claim this calculator makes about your number.
The body shape index formula, in the open
The A Body Shape Index formula is published and unpatented, so here it is rather than hidden behind the calculator. Every ABSI calculation on this page uses exactly this, and the worked example further down shows the arithmetic with real numbers.
ABSI = WC / (BMI2/3 x height1/2), with waist circumference and height in meters and BMI computed from weight in kilograms. Algebraically this equals WC x weight-2/3 x height5/6, the form used in the original authors' own calculator and in this implementation (the two are verified equal in our automated tests). Typical adult values land near 0.08, which is why results are shown to four decimal places; small numeric differences are meaningful at this scale. The "how this was calculated" panel under your result substitutes your actual numbers into the formula, so nothing about the computation is a black box, and the same transparency section of our editorial standards applies here as everywhere on this site.
How the z-score works
Raw ABSI varies systematically with age and sex, so comparing your value against the right reference group matters. This calculator uses the smoothed age- and sex-specific means and standard deviations for ages 2 through 85 published by the index's original authors from NHANES 1999-2004 data, embedded verbatim with their source cited in our code. Your z-score is (your ABSI minus the reference mean for your age and sex) divided by the reference standard deviation, and the result panel shows you the exact mean and SD used, so the arithmetic is checkable. The accompanying band ("close to the reference average", "well above" and so on) describes position in that reference distribution using conventional quintile boundaries. Ages beyond 85 use the age-85 row, matching the original calculator's behavior, and the tool tells you which reference age it applied. What the z-score is not: a risk grade, a diagnosis, or a statement about you as an individual. It is a comparison with a specific American reference population from a specific period, which is also why results can differ slightly from tools that use other references.
ABSI as a body shape calculator for men and women
People searching for a body shape calculator usually find one of two very different tools, so it is worth being clear about which this is. Many body shape calculators are styling tools: they take bust, waist, and hip measurements and sort you into categories like hourglass, pear, or rectangle, mostly for clothing fit. This page is the other kind: a numeric body shape index. ABSI literally stands for A Body Shape Index, and it quantifies shape as a single number from waist, height, and weight, comparable against published reference data. That makes it especially useful as a body shape calculator for men, who are poorly served by dress-silhouette categories: a male body shape calculation here means an objective waist-relative-to-build number and an age-matched z-score, not a fruit metaphor. It works identically for women, using the female reference table, and for anyone tracking how their shape, rather than just their weight, changes over time. If you came here wanting the hourglass-versus-pear kind of answer, this tool will not give you one; if you want a measurable, trackable shape metric grounded in research, you are in the right place.
What is a good ABSI score?
ABSI has no official clinical cutoffs, so beware of any page that hands you a pass or fail grade. What exists instead is a reference distribution. Most adults land roughly between 0.07 and 0.09, and your z-score places you precisely within your age and sex group. Interpreted honestly, the bands look like this:
| Z-score | Position in the reference population |
|---|---|
| below -0.87 | Well below the reference average |
| -0.87 to -0.27 | Below the reference average |
| -0.27 to +0.23 | Close to the reference average |
| +0.23 to +0.80 | Above the reference average |
| above +0.80 | Well above the reference average |
In the research, lower-than-average ABSI sits in the range associated with lower observed mortality hazard at the population level, and higher-than-average with higher hazard. That is an association across thousands of people, not a verdict on you, which is why "is my score good?" has a better replacement question: "is my trend stable or moving in the direction I want?" A single reading is a data point; three months of consistent measurements is information. There is also no meaningful "normal range" to chase beyond the reference bands above, because the reference itself is simply the measured American population, not a health target.
How to calculate ABSI by hand
The calculator above does this instantly, but the arithmetic is checkable with any scientific calculator, and seeing it once demystifies the number. Take a person weighing 80 kg, 175 cm tall, with a 90 cm waist. Step one: BMI = 80 / 1.752= 26.1. Step two: raise BMI to the power 2/3: 26.12/3 = 8.80. Step three: square root of height in meters: sqrt(1.75) = 1.32. Step four: divide the waist in meters by the product: 0.90 / (8.80 x 1.32) = 0.0773. That is the ABSI. For the z-score, subtract your age and sex reference mean and divide by the reference standard deviation; for a 30-year-old man (mean 0.07941, SD 0.00352) this example gives (0.0773 - 0.07941) / 0.00352 = -0.61, or somewhat below the reference average. Every number in that chain is visible in the tool's "how this was calculated" panel with your own inputs substituted.
How to measure your waist properly
ABSI inherits the quality of your tape measurement, so technique matters more than any other input. Use a flexible, non-stretch tape. Stand relaxed with weight even on both feet, breathe out normally, and take the reading at the end of that exhale. Keep the tape horizontal all the way around, snug against the skin without compressing it. Research protocols differ on the exact landmark (some use the top of the hip bone, others the midpoint between the lowest rib and the iliac crest, others the navel), and those landmarks can differ by a centimeter or more on the same person. For this calculator's purpose, the practical rule is: pick one landmark, note it, and use it every time, at the same time of day under similar conditions. Consistent technique is what makes your saved trend interpretable; a mixture of landmarks makes it noise.
ABSI vs BMI vs waist-to-height ratio
The three numbers this tool reports answer different questions. BMI relates weight to height: it is the simplest and most studied, but it treats a kilogram of muscle and a kilogram of abdominal fat identically. Waist-to-height ratio brings in the waist with an easy rule of thumb but ignores weight entirely. ABSI is the statistically fancier construction: waist adjusted for both height and weight, built to be independent of BMI. The evidence positions them as complements rather than competitors. A 2018 meta-analysis found higher ABSI associated with hypertension, type 2 diabetes, cardiovascular disease, and all-cause mortality, and reported that ABSI outperformed BMI and waist circumference for all-cause mortality association while underperforming for some chronic-disease outcomes. Later studies across different populations show varying strength of association, which is exactly why no single index deserves to be treated as a universal verdict. Seeing all three together, as this calculator shows them, is more informative than any one alone.
Limitations, stated plainly
Every honest measurement tool should list what it cannot do. ABSI is sensitive to waist-measurement technique, so sloppy or inconsistent taping produces misleading values and trends. The reference data are from a US population sampled between 1999 and 2004; z-scores against that reference are less meaningful for populations that differ from it, and no universal threshold applies everywhere. Mortality hazard ratios from epidemiological studies are statements about groups, not probabilities about you. And because ABSI is derived from external measurements, it cannot see body composition directly: no tape measure can. This is also why our history feature emphasizes the trend line over any single reading, and why each saved record stores the methodology version and reference values it was computed with.
Original research and validation
- Krakauer NY, Krakauer JC (2012): A New Body Shape Index Predicts Mortality Hazard Independently of Body Mass Index (PLoS ONE, the original paper)
- Ji M, et al. (2018): Meta-analysis of ABSI and health outcomes (PubMed)
- Krakauer & Krakauer (2014): Dynamic association of mortality hazard with body shape
- Reference data source: the original authors' public ABSI calculator (NHANES 1999-2004 smoothed age/sex means and SDs, embedded verbatim in this tool)