ABSI Calculator
This ABSI calculator answers one question: is your waist thick for the body it sits on? You enter height, weight, waist, sex and age, and the card returns the raw A Body Shape Index at five decimals, an age- and sex-adjusted absi z score at two, and a quintile band from Very low to Very high. A BMI and a waist-to-height ratio ride along in the same card as cross-checks, because the absi index is built by adding the waist to the BMI — reading all three together is the honest way to use it. One sentence before the numbers: the absi score is a research index derived on a specific reference population, it is not a diagnostic cutoff, and the z score says where you sit in that population rather than what will happen to you.
Measurements
A Body Shape Index
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The z-score uses the NHANES 1999–2004 US adult reference distribution. South and East Asian populations can show metabolic risk at lower ABSI values, so treat this band as conservative.
What the ABSI Calculator Measures
ABSI stands for A Body Shape Index, and it was proposed by Nir Krakauer and Jesse Krakauer in 2012 (PLoS ONE) as a way to bring the waist into the BMI conversation without the waist simply restating the BMI. The two exponents in the formula were fitted on the paper’s reference sample so that the raw value stays close to independent of the BMI — that is the property that lets it add information rather than repeat the same signal. The body mass index sees how heavy you are for your height; a body shape index calculator asks how that weight is arranged around the middle, and the two answers do not have to agree.
Why the card prints two numbers. The raw index and the z score do different jobs. The raw ABSI is the definition value — the number printed in the literature, which is why the headline keeps five decimals (0.07978, not 0.08) — but it has no unit you can interpret by eye: it is the waist in metres divided by the BMI to the power 2/3 and the square root of the height in metres, which simplifies to m11/6·kg−2/3, a unit nobody carries in their head. A raw value near 0.08 is a typical adult reading; there is no “good” or “bad” attached to the raw number itself. The z score is the readable version: it says how far your ABSI sits from the mean of a reference group with your sex and age band, measured in units of that group’s standard deviation. Both count as displayed values on the card, and the equation row shows the arithmetic that connects them.
What the quintile band is, and is not. The badge above the z score is a quintile label, and it is worth being precise about that. The four cut-points were placed so that each of the five bands holds about 20% of the reference population by construction — so one adult in five is above the “Very high” line by definition and one in five is below “Very low”. “High” therefore means the fourth fifth of that population, not a danger line, and “Low” means the second fifth, not automatically good news. The band answers the question “where do I sit relative to this population”, and a band describes a population rather than a person — two people with the same z score can have very different bodies.
The reference table itself is an adult table. Below 20 years old there is no matching age band, so the card falls back to the 20–29 row and labels it “closest band — ABSI is an adult index”; at the other end, the 70+ row is the final band and covers everyone older. The tool is not a children’s calculator, which is also why age is a required field: without it the reference row cannot be chosen, and using one all-ages average would systematically misplace older users.
The ABSI Formula, the Z Score and the Reference Table
The absi formula is one division, and everything else on the card is either derived from it or looked up in the reference table:
\[ \text{ABSI} = \frac{\text{waist (m)}}{\text{BMI}^{2/3} \times \text{height (m)}^{1/2}} \]
The BMI in the denominator is the familiar weight-over-height-squared ratio, computed from the same height and weight you enter:
\[ \text{BMI} = \frac{\text{weight (kg)}}{\text{height (m)}^{2}} \]
Substituting that into the definition and simplifying gives a form that shows what moves the number:
\[ \text{ABSI} = \frac{\text{waist (m)} \times \text{height (m)}^{5/6}}{\text{weight (kg)}^{2/3}} \]
Read the exponents, because they are the whole design. The absi index is proportional to the waist — a 1% larger waist gives a 1% larger ABSI, exactly — while the weight enters with a negative power, so a heavier body at the same waist lowers the value, and the height enters with a positive one. That is what “shape” means here: the tape reading is judged against the mass and length of the body carrying it, not in absolute centimetres.
The raw value is then standardised against the reference row for your sex and age band:
\[ z = \frac{\text{ABSI} – \mu_{\text{sex, age band}}}{\sigma_{\text{sex, age band}}} \]
where \(\mu\) is the reference mean and \(\sigma\) the reference standard deviation from this table, published in the 2012 paper from the adult sample behind it:
| Age band | Men: mean ± SD | Women: mean ± SD |
|---|---|---|
| 20–29 | 0.0789 ± 0.0049 | 0.0762 ± 0.0048 |
| 30–49 | 0.0805 ± 0.0051 | 0.0780 ± 0.0050 |
| 50–69 | 0.0824 ± 0.0053 | 0.0805 ± 0.0053 |
| 70+ | 0.0843 ± 0.0055 | 0.0827 ± 0.0056 |
These are reference values, not targets: they describe where the adult sample sat, and the women’s rows run slightly lower than the men’s at every age. Note also that the means climb with age — a man’s average moves from 0.0789 in his twenties to 0.0843 past 70 — so the same raw ABSI is judged against a different yardstick at 25 and at 75. That drift is exactly why the z score is the number the bands are cut from.
The z score is cut into five quintile bands. The label is what the badge and the “Risk quintile” row print:
| ABSI z score | Band | Share of the reference population |
|---|---|---|
| below −0.868 | Very low | the bottom 20% by construction |
| −0.868 to below −0.272 | Low | about 20% by construction |
| −0.272 to below +0.229 | Average | about 20% by construction |
| +0.229 to below +0.798 | High | about 20% by construction |
| +0.798 and above | Very high | the top 20% by construction |
Every quantity the card prints has a symbol, a meaning and a fixed role — this table lists them together:
| Symbol | Meaning | How it is used |
|---|---|---|
| ABSI | the raw a body shape index value | the headline, waist(m) ÷ (BMI^(2/3) × height(m)^(1/2)), printed to five decimals |
| BMI | body mass index | weight ÷ height², printed to one decimal for comparison |
| z | the standardised absi z score | (ABSI − reference mean) ÷ reference SD, printed to two decimals |
| μ | reference mean | read from the sex × age band row of the reference table |
| σ | reference standard deviation | read from the same row |
| WHtR | waist-to-height ratio | waist ÷ height, printed to two decimals as a cross-check |
Metric and imperial entries reach the same numbers, because everything is converted before the division runs — an imperial height is split into feet and inches rather than one decimal field:
\[ \text{height (cm)} = \text{height (in)} \times 2.54, \qquad \text{weight (kg)} = \text{weight (lb)} \times 0.4536, \qquad \text{waist (cm)} = \text{waist (in)} \times 2.54 \]
Precision and boundaries. Only positive numbers are accepted, and every field has a wide sanity range: age 2 to 120 years, height 50 to 260 cm (1 ft 8 in to 8 ft 6 in), weight 10 to 500 kg (22 to 1102 lb) and waist 30 to 250 cm (12 to 98 in). Results are rounded for display: the raw ABSI to five decimals, the absi z score to two, the BMI to one and the waist-to-height ratio to two. When a field cannot be used, the card keeps the previous result on screen and adds one line naming the reason: “Please enter a valid number.” for an empty or non-numeric field; “Age must be between 2 and 120 years.” for an age outside its range; “Height is out of range — enter 50 to 260 cm (1 ft 8 in to 8 ft 6 in).” and “Waist is out of range — enter 30 to 250 cm (12 to 98 in).” for a measurement outside its range; and, as the last fallback, “The result is out of range for these inputs.”
How to Use the ABSI Calculator
- Pick the unit system first. Metric takes centimetres for height and waist and kilograms for weight; imperial reads height as two fields, feet plus inches, because 5.11 ft is not 5 ft 11 in, and reads weight in pounds and the waist in inches. Switching units converts the values already typed, so a figure entered in centimetres cannot silently turn into an absurd imperial one.
- Choose sex. This selects the reference row, and it changes the reading rather than just the label — the women’s table sits lower than the men’s at every age band.
- Enter age (required). The band lookup depends on it, and the accepted range is 2 to 120 years. Under 20 the card uses the 20–29 row and says so on the reference line; 70 and over is the final band.
- Enter height, weight and waist. For the waist, run a cloth tape midway between the lowest rib and the top of the hip bone — for most people roughly level with the navel — after a normal exhale, keeping the tape level and snug without compressing the skin. Measure twice and keep the routine identical, because a tape that rides up moves the reading more than most people expect.
- Read the card top to bottom. The headline is the raw index at five decimals; the line beneath it is the equation that produced the z score; the badge is the quintile band. Below that, the ABSI z-score row repeats the z with its band, the reference row names the exact sex and age band used, and the BMI and waist-to-height ratio rows give you the two comparison readings.
- Reset if you want the starting card. The reset button restores the preset the page opens on — age 45, male, 175 cm, 70 kg, 85 cm — which is also the first worked example below.
- Copy or export. One copy button takes the headline number alone and the other takes the summary plus the equation line. The card can also be exported as an image or a PDF, and the QR code in the exported file encodes this page together with your inputs, so scanning it reopens the calculator with the same numbers already filled in.
Worked Examples
Three cards, all computed by the tool’s own metric branch. Each row below quotes what the calculator prints, character for character, so the arithmetic can be checked line by line.
Example 1 — a 45-year-old man, 175 cm, 70 kg, 85 cm waist
This is the preset the page opens on. The headline is the raw index at five decimals — 0.07978 — and the equation row carries the conversion against the male 30–49 reference row, whose mean is 0.0805 and whose standard deviation is 0.0051: “z = (0.07978 − 0.0805) ÷ 0.0051 = -0.14”. A z of about -0.14 is a seventh of a standard deviation below the reference mean, which lands in the Average quintile. The summary line, which is what the copy button hands you, reads: “ABSI 0.07978, z-score -0.14 (Average) — BMI 22.9 for comparison”. The comparison rows come from the same inputs: BMI 22.9 is 70 ÷ 1.75², and the waist-to-height ratio of 0.49 is 85 ÷ 175 — right at the 0.5 line. On a tape in inches, 175 cm is about 5 ft 9 in (the imperial fields show it as 5 ft 8.9 in) and 85 cm is roughly 33.5 in.
| Line on the card | What it shows |
|---|---|
| Headline (raw ABSI) | 0.07978 |
| ABSI z-score (age- and sex-adjusted) | -0.14 — Average |
| Reference mean and SD (this sex and age band) | 0.0805 ± 0.0051 — men, 30–49 |
| BMI (for comparison) | 22.9 — normal |
| Waist-to-height ratio (for comparison) | 0.49 |
| Risk quintile | Average |
| What the band means | with the reference population, each band holds 20% by construction |
Example 2 — a 45-year-old man, 180 cm, 95 kg, 102 cm waist
Same age, same sex, a bigger body. The raw index comes out marginally higher — 0.07995 — and the equation reads “z = (0.07995 − 0.0805) ÷ 0.0051 = -0.11”, still about a tenth of a standard deviation below the male 30–49 mean and still the Average quintile. This is the example worth sitting with, because the comparison rows disagree with the band: the BMI line reads “29.3 — overweight” and the waist-to-height ratio of 0.57 is in the increased-risk range of the NICE bands, while the absi score keeps an average z score. That is not a contradiction — the index asks whether the waist is thick for this particular body, and 102 cm does not read as disproportionate on a 180 cm, 95 kg frame. The summary line reads: “ABSI 0.07995, z-score -0.11 (Average) — BMI 29.3 for comparison”.
| Line on the card | What it shows |
|---|---|
| Headline (raw ABSI) | 0.07995 |
| ABSI z-score (age- and sex-adjusted) | -0.11 — Average |
| Reference mean and SD (this sex and age band) | 0.0805 ± 0.0051 — men, 30–49 |
| BMI (for comparison) | 29.3 — overweight |
| Waist-to-height ratio (for comparison) | 0.57 |
| Risk quintile | Average |
| What the band means | with the reference population, each band holds 20% by construction |
Example 3 — a 35-year-old woman, 165 cm, 60 kg, 75 cm waist
The third card switches sex and drops into the 30–49 band from the other side: a woman of 35. Her raw index is the lowest of the three — 0.07428 — and the equation uses the women’s 30–49 row, whose mean (0.0780) and SD (0.0050) are both lower than the men’s: “z = (0.07428 − 0.0780) ÷ 0.0050 = -0.74”. Three-quarters of a standard deviation below the reference mean is the Low quintile, the second band from the bottom, and the summary line reads: “ABSI 0.07428, z-score -0.74 (Low) — BMI 22.0 for comparison”. Her BMI of 22.0 is nearly the same as the first example’s 22.9, which is the cleanest illustration of why these indices are read together: the same weight-for-height sits at different places on the shape scale, because the ABSI compares the waist with the body that carries it and because the female reference row is lower.
| Line on the card | What it shows |
|---|---|
| Headline (raw ABSI) | 0.07428 |
| ABSI z-score (age- and sex-adjusted) | -0.74 — Low |
| Reference mean and SD (this sex and age band) | 0.0780 ± 0.0050 — women, 30–49 |
| BMI (for comparison) | 22.0 — normal |
| Waist-to-height ratio (for comparison) | 0.45 |
| Risk quintile | Low |
| What the band means | with the reference population, each band holds 20% by construction |
None of the three examples lands in the High or Very high band, and that is worth stating plainly rather than hiding: they were chosen as ordinary cases, not as extremes. The lines that would move them there are in the quintile table above — High begins at a z of +0.229 and Very high at +0.798 — and because the equation row always prints the subtraction and division, you can see exactly how far any card sits from either line.
ABSI Calculator FAQ
What is ABSI?
ABSI stands for A Body Shape Index — a waist-based research index introduced by Krakauer and Krakauer in 2012 that adds the waist to the BMI instead of replacing it. The raw value has no everyday meaning on its own, so this absi calculator converts it into a z score against a reference table for your sex and age band and prints the quintile band that z score falls into, together with a BMI and a waist-to-height ratio for comparison.
How is the ABSI score calculated?
The absi score is one division: the waist in metres divided by the BMI to the power 2/3, multiplied by the square root of the height in metres. The result is then standardised — the reference mean for your sex and age band is subtracted and the difference is divided by that band’s standard deviation — which is what turns an unreadable raw number into the z score the bands are cut from. Nothing is estimated or smoothed: the headline is that division at five decimals, and the equation row shows the two operations that produce the z.
What does the ABSI z score mean?
A z score of -0.14 means your ABSI sits 0.14 standard deviations below the mean of the reference group for your sex and age band. It is a position, not a verdict, and it is also what the quintile label is cut from: below -0.868 is Very low, below -0.272 is Low, below +0.229 is Average, below +0.798 is High, and +0.798 or above is Very high. A z of 0 means you sit exactly at the reference average for people like you in that table.
Is there a healthy ABSI range?
There is no single healthy ABSI number to aim for, because the index was built to be read against a reference population rather than against a fixed cutoff. The five quintile bands each hold about 20% of that reference population by construction, so one adult in five is above the Very high line by definition and one in five sits below Very low — being in a band says where you are in a distribution, not what your health is. The practical use is to track your own number over time, and to read it next to the BMI and waist-to-height ratio rows, which look at the same body from different angles.
Is ABSI better than BMI?
No — it answers a different question, and the two are meant to be read side by side rather than as a winner and a loser. The BMI compares weight with height and cannot see where the weight sits; the ABSI puts the waist into the calculation and asks whether that waist is thick for the body carrying it. Example 2 on this page shows the split concretely: a BMI of 29.3 reads overweight while the absi score keeps an average z score, because the waist is proportional to a large frame — one reading flags the weight itself, the other says the shape is unremarkable.
Why is the ABSI reference table split by sex and age?
Because the average ABSI rises with age and differs between men and women, so the same raw value lands in a different place depending on who you are. In the reference table a man’s mean moves from 0.0789 in his twenties to 0.0843 past 70, and the women’s rows run slightly lower at every band — a raw reading that sits at the average for a 75-year-old would be above average for a 25-year-old. That is why age is a required field and why the card prints the exact sex and age row it used on the reference line.
Does the ABSI calculator work in pounds and feet?
Yes. In imperial mode the height is entered as feet plus inches in two separate fields, weight is read in pounds and the waist in inches, and everything is converted to centimetres and kilograms internally before the formula runs. Switching units converts the values already entered, so a figure typed in centimetres cannot silently become a mismatched imperial one — 175 cm arrives in the imperial fields as 5 ft 8.9 in, the same body rather than a rounded 5 ft 9 in.
Related Tools
The pages around this one all take the tape measure somewhere else. The waist-to-height ratio calculator divides the waist by height alone and checks it against the NICE bands — the simplest height-scaled reading of the same tape, and the ratio this card already prints as its own comparison line. The BAI calculator swaps the waist for the hips and estimates body fat share from hip circumference and height with no scale involved, which is the version to reach for when weight is not available. The enhanced BMI calculator stays with weight and height but surrounds the same BMI with BMI Prime, the ponderal index, body surface area, body fat, lean mass, BMR, TDEE and calorie targets. And if you would rather see everything on one screen — the BMI plus twelve indicator cards, ABSI included — the body dashboard lays them out together.
