The ABSI calculator above computes A Body Shape Index exactly as it is defined in the paper that introduced it, and then stops. It gives you the number, the BMI term inside it, the waist the reference sample would predict for someone of your height and weight, and how far your measured waist sits from that in standard deviations. It does not label the result, does not place you in a band, and does not tell you anything about your health.
Arb Digital builds free calculators that name their sources and state their limits. ABSI is a research index rather than a clinical standard, and the honest way to publish it is to compute it faithfully, say where it came from, and leave interpretation to the people qualified to do it.
What This ABSI Calculator Does
You enter waist circumference, height and weight in either metric or imperial units. The tool converts everything to metres and kilograms, builds BMI, and applies the published ABSI formula. The headline is the raw ABSI value, which is a small number with several decimal places because of the units the formula uses.
Underneath, four supporting figures. The BMI the formula used, so you can see the ingredient rather than guessing at it. The waist circumference that the reference mean ABSI would predict for your height and weight, which is the most intuitive way to read the index. The simple ratio of your measured waist to that expected waist. And the number of standard deviations between your ABSI and the reference mean, using the mean and standard deviation you can edit in the panel.
That last figure is a position within a stated distribution. It is not a score, not a grade, and not a statement about risk.
Where the Formula Comes From
ABSI was introduced by Nir Y. Krakauer and Jesse C. Krakauer in A New Body Shape Index Predicts Mortality Hazard Independently of Body Mass Index, published in PLOS ONE in July 2012. The paper derived the index from a United States population sample of 14,105 non-pregnant adults drawn from the National Health and Nutrition Examination Survey for 1999 to 2004, with mortality follow-up averaging about five years and 828 deaths recorded.
The paper reports a sample mean ABSI of 0.0807 with a standard deviation of 0.0041, which is where the defaults in the reference fields come from. Those two numbers describe that specific sample of United States adults in that period. They are not universal constants, and the authors themselves work with age- and sex-specific values rather than a single pooled figure.
What ABSI was derived to do is narrow and worth stating plainly: it was constructed so that waist circumference could be assessed independently of height and weight, and it was evaluated as a predictor of mortality hazard in that cohort. That is a population-level statistical property. It is not a diagnostic test, it is not endorsed as a clinical measure by health authorities in the way BMI thresholds are, and a single value calculated for one person says nothing on its own.
The Formula / How It's Calculated
The published definition is ABSI = WC ÷ (BMI2/3 × height1/2), with waist circumference and height in metres and BMI in the usual kilograms per square metre. The fractional exponents are the point of the whole thing: they are chosen so that the resulting index has essentially no correlation with height or weight, which is what lets it carry information BMI does not.
Work through the defaults by hand. A waist of 90 cm is 0.90 m, height 175 cm is 1.75 m, weight is 75 kg. BMI is 75 ÷ 1.75² = 75 ÷ 3.0625 = 24.49. Raise that to the power two-thirds and you get 8.4321. The square root of 1.75 is 1.32288. Multiply those and the denominator is 11.1547. So ABSI = 0.90 ÷ 11.1547 = 0.08067.
Against a reference mean of 0.0807 and standard deviation of 0.0041, that is (0.08067 − 0.0807) ÷ 0.0041 = −0.01 standard deviations — essentially sitting on the sample mean. Turning it round, the waist the reference mean predicts for this height and weight is 0.0807 × 11.1547 = 0.9003 m, or about 90.0 cm, which is what the measured waist happens to be.
That worked example is a useful sanity check on any implementation. If a calculator gives you something other than roughly 0.0807 for a 90 cm waist at 175 cm and 75 kg, it has a unit error somewhere — almost always centimetres left where metres belong.
How ABSI Differs From BMI, Body Fat and Waist Ratios
This matters, because there are several adjacent tools and they are genuinely measuring different things. Our BMI calculator divides weight by height squared and reports the standard categories that health services publish; it says nothing about where mass sits on the body. Our body fat calculator uses the US Navy circumference equations to estimate a fat percentage, and our skinfold body fat calculator estimates the same quantity from caliper measurements. Both of those are attempts to measure composition.
ABSI is not attempting either. It is a shape index. It asks whether your waist is larger or smaller than the waist a population sample would predict for a person of your height and weight, and expresses that as a single number. Two people with identical BMI and identical body fat percentage can have quite different ABSI values, and that difference is the whole information content of the index.
The simpler waist ratios are closer cousins. Our waist-to-height ratio calculator divides waist by height and compares against widely published thresholds, and the waist-to-hip ratio calculator compares two circumferences to each other. Both are simpler than ABSI, both are easier to interpret, and both are used more widely in practice. ABSI's specific claim is that its exponents remove the residual dependence on height and weight that a plain waist-to-height ratio still carries. Whether that extra step earns its complexity is an open question in the literature, not a settled one.
Measurement Error Is the Biggest Source of Variation
ABSI is dominated by one measurement, and that measurement is harder to take consistently than people expect. The World Health Organization expert consultation report on waist circumference and waist-hip ratio devotes substantial attention to exactly this: where on the torso the tape goes, whether it is taken at the narrowest point or at the midpoint between the lowest rib and the iliac crest, at what point in the breathing cycle, over clothing or against skin, and how much those choices move the result.
They move it by a lot. A two-centimetre difference in tape placement is easy to produce and shifts ABSI by roughly two per cent, which is around half a standard deviation of the reference sample. If you are tracking a number over months, an inconsistent protocol will generate changes larger than anything real. Measure at the same anatomical landmark, at the same time of day, at the end of a normal exhalation, with the tape horizontal all the way round, and repeat it two or three times and average.
The same report also documents that the relationship between waist measurements and health outcomes varies by sex and by ethnic group, and that cut-off points developed in one population do not transfer cleanly to another. That is a general caution about every circumference-based index, ABSI included.
Reading the Standard Deviation Figure Honestly
The reference mean and standard deviation on this page come from one national survey sample of United States adults over a five-year window ending in 2004. A z-score against them tells you where you sit relative to that sample. It does not tell you where you sit relative to adults in your own country today, relative to people your age, or relative to people of your sex — ABSI shifts systematically with all three, which is why the original paper builds age- and sex-specific reference values rather than using one pooled figure.
Both fields are editable for that reason. If you have reference values that fit the population you are actually working with, put them in and the z-score will mean something closer to what you want. If you do not, read the figure as "distance from the mean of a 1999–2004 US adult sample" and nothing more.
It is also worth remembering what a z-score is not. It is not a percentile of health, it is not a risk multiplier, and a value above or below zero carries no verdict. If you want the general statistics behind it, our z-score calculator and percentile calculator cover how these figures behave.
What No Body Index Can Tell You
No single number describes an individual's body, and ABSI is a particularly narrow one: it uses three measurements and reduces them to one figure. Body composition varies with ancestry, muscle mass, bone structure, age, sex, hydration and where fat is distributed for reasons that have nothing to do with behaviour. A very muscular person and a sedentary person can produce similar values by different routes, and a value at the population mean is not evidence that anything is or is not fine.
ABSI is also, at the time of writing, a research index. It has been studied in a substantial number of cohorts since 2012, with mixed and sometimes conflicting findings, and it is not used as a clinical threshold by national health services in the way BMI and waist circumference are. Treating a research index as if it were a diagnostic tool is the single biggest error available on this topic.
If a number on this page concerns you, or you are trying to understand your own measurements, the person to talk to is a clinician who can see the whole picture — history, bloods, family history, symptoms, activity, everything a calculator cannot see.
Arb Digital designs and builds free interactive calculators that cite the paper behind the formula, state what the formula cannot do, and stay on the right side of the line between information and advice. Browse what we have already published, or tell us what your audience keeps searching for.
Browse the Free Tools Hub Talk to Arb DigitalCommon Mistakes to Avoid
- Leaving centimetres in the formula. ABSI is defined with waist and height in metres. Using centimetres produces a value roughly a hundredth of the size and makes every comparison meaningless.
- Treating the reference mean as a target. 0.0807 is the mean of one US survey sample, not a goal, a threshold or a healthy value.
- Changing where you put the tape. Waist protocol differences of a couple of centimetres swamp real change. Fix one landmark and use it every time.
- Reading a z-score as a risk statement. It reports distance from a sample mean. It carries no clinical meaning on its own.
- Using ABSI in place of BMI or body fat. They answer different questions. ABSI describes shape relative to expectation, not mass and not composition.
Related Free Tools From Arb Digital
Compare with the BMI calculator for the standard published categories, the body fat calculator and skinfold body fat calculator for composition estimates, the waist-to-height ratio calculator and waist-to-hip ratio calculator for the simpler circumference ratios, the body roundness index calculator and body adiposity index calculator for the other geometric indices, and the z-score calculator for the statistics. Everything else is on the free online tools hub.
Frequently Asked Questions
A Body Shape Index is waist circumference divided by BMI raised to the power two-thirds multiplied by the square root of height, with waist and height in metres and BMI in kilograms per square metre. It was defined that way by Krakauer and Krakauer in PLOS ONE in 2012.
This page does not define one. The originating paper reports a sample mean of 0.0807 with a standard deviation of 0.0041 for 14,105 US adults surveyed between 1999 and 2004. That describes a sample, not a healthy range, and no category label is attached here.
BMI relates weight to height and says nothing about where mass sits. ABSI compares measured waist circumference with the waist a population would predict for that height and weight, so two people with identical BMI can have very different ABSI values.
It is a research index rather than a clinical standard. It has been studied in a number of cohorts since 2012 with mixed findings, and it is not published as a diagnostic threshold by national health services the way BMI and waist circumference are.
Waist circumference is the dominant term in the formula. A two-centimetre difference in tape placement moves ABSI by roughly two per cent, which is about half the standard deviation of the reference sample, so protocol consistency matters more than precision of the arithmetic.
Yes, both fields are editable. The defaults are the pooled figures from the originating paper's US sample, and the paper itself uses age- and sex-specific values, so a reference that matches your population will give a more meaningful z-score.
This page makes no such statement and attaches no risk to any value. ABSI is one number derived from three measurements, body composition varies for many reasons, and interpreting any body measurement is a matter for a qualified clinician.
This page is a calculation tool for general information only. It is not medical advice, it does not diagnose or assess any condition, and it attaches no health category or risk statement to any result. A Body Shape Index is a research index, not a clinical standard. If you have questions about your weight, your measurements or your health, speak to a qualified clinician.
