A Body Shape Index (ABSI) Calculator
Compute your A Body Shape Index (ABSI), the age- and sex-adjusted z-score, and the mortality-risk band — a measure of central adiposity that is statistically independent of BMI.
ABSI — Low mortality risk
0.07728
- Age/sex-adjusted z-score
- -0.49
- Expected ABSI for your age/sex
- 0.07962
- BMI (for reference)
- 26.1
- Waist-to-height ratio
- 0.514
ABSI = waist (m) ÷ (BMI^(2/3) × √height (m)). It captures central adiposity in a way that is statistically independent of BMI — two people with the same BMI can have very different ABSI values depending on how the weight is distributed. The z-score compares your ABSI to the NHANES 1999–2004 mean for your age and sex (Krakauer 2012, PLoS ONE); risk bands are the quintile cut-offs from Krakauer 2014. ABSI predicts premature mortality independently of BMI but is a population-level signal, not a clinical diagnosis.
How to use this calculator
Choose metric or imperial units, pick your sex, then enter your age, weight, height and waist circumference. The calculator returns your raw ABSI value to five decimal places, the z-score comparing it to the NHANES reference distribution for your age and sex, the expected (mean) ABSI for that group, plus your BMI and waist-to-height ratio for context. The headline label tells you which of the five mortality-risk bands the z-score puts you in.
How the calculation works
ABSI is defined as waist circumference (m) divided by BMI raised to the two-thirds power times the square root of height (m): ABSI = WC ÷ (BMI^(2/3) × √height). The two-thirds exponent on BMI and the half-power on height are chosen so the resulting index is statistically uncorrelated with both — meaning ABSI captures shape information that BMI cannot. Imperial inputs are converted using NIST-exact factors (1 lb = 0.45359237 kg, 1 in = 0.0254 m). The z-score subtracts the age- and sex-specific mean ABSI from Krakauer 2012 Table 1 (NHANES 1999–2004 US adults) and divides by the same group's standard deviation. Risk bands come from Krakauer 2014: very low below z = −0.868, low to −0.272, average to +0.229, high to +0.798, and very high above that.
Worked example
A 50-year-old man, 1.75 m tall, 80 kg, with a 90 cm waist. BMI = 80 ÷ 1.75² = 26.12. ABSI = 0.90 ÷ (26.12^(2/3) × √1.75) = 0.90 ÷ (8.804 × 1.3229) = 0.90 ÷ 11.648 = 0.07727. The reference mean for men aged 50–59 is 0.08113 with an SD of 0.00499, so the z-score is (0.07727 − 0.08113) ÷ 0.00499 = −0.77 — below average for his age and sex, putting him in the low mortality-risk band.
Frequently asked questions
What is ABSI and why does it matter?
ABSI — A Body Shape Index — was introduced by Krakauer and Krakauer in 2012 as a way to capture central (abdominal) adiposity that is statistically uncorrelated with BMI. Two people with the same BMI can have very different ABSI values: a person with a thick waist relative to their overall size scores higher. In the original NHANES study and several follow-ups, higher ABSI predicted premature mortality independently of BMI, waist circumference alone, and the waist-to-height ratio. It is a population-level risk signal, not a clinical diagnosis.
What is a healthy ABSI value?
Raw ABSI values cluster around 0.07–0.09 for adults and shift upward with age, so the raw number alone does not tell you much. The z-score does: it compares your ABSI to the published mean for your age and sex. A z-score below 0 means your central adiposity is lower than the population average; above 0 means higher. The Krakauer 2014 risk bands split the z-score into five categories — very low, low, average, high and very high — using the published quintile cut-offs.
How is ABSI different from BMI or waist-to-height ratio?
BMI captures overall size relative to height but cannot distinguish a lean, muscular build from a thick-waisted one of the same weight. Waist-to-height ratio (WHtR) does capture waist size but still correlates strongly with BMI. ABSI was specifically constructed so that, on average, knowing someone's BMI tells you nothing about their ABSI — the exponents on BMI and height in the formula are tuned to remove that correlation. That makes ABSI a complementary metric you read alongside BMI, not a replacement.
How should I measure my waist?
Use a non-stretch tape measure. Stand relaxed with your feet shoulder-width apart and arms at your sides, breathing normally. Wrap the tape horizontally around your torso at the midpoint between the lower edge of your ribs and the top of your hip bone (iliac crest) — this is the WHO-recommended landmark. Measure at the end of a normal exhale, not while sucking in. Record to the nearest 0.5 cm or 0.25 inch.
Does ABSI work for athletes, pregnant women or children?
ABSI inherits the limitations of BMI for these groups. Very muscular athletes can have an inflated BMI, which affects the ABSI calculation; ABSI is not validated in heavily trained populations. It is not valid during pregnancy — waist measurements no longer reflect adiposity. The reference distribution embedded in this calculator is for adults aged 18 and over; the calculator rejects ages below 18 because no validated paediatric ABSI norms exist.
Is ABSI a substitute for medical advice?
No. ABSI is a research metric that summarises a population-level relationship between body shape and mortality risk. It does not diagnose any condition and does not replace blood pressure, lipid panel, glucose, or clinical examination. If your z-score falls in the high or very-high band, treat it as one signal among many — useful for asking your clinician informed questions, not for self-medicating.