A Body Shape Index - Krakauer ABSI, Z-Score & Hazard Ratio

A body shape index (ABSI) is a single number that summarises how much of a person's waist circumference is left over after accounting for their height and overall mass. It was developed by Nir Krakauer and Jesse Krakauer in 2012 as a complement to BMI, on the idea that central adiposity carries risk that BMI alone does not capture.

• • Adding context to BMI: Two adults with the same BMI can carry very different amounts of abdominal fat. ABSI surfaces that difference and helps the reader decide whether a normal BMI is really a low-risk BMI.
• • Tracking risk over time: Re-entering measurements every few months shows whether waist changes are improving or worsening the index, even when body weight is stable.
• • Comparing peers in plain language: ABSIs for adults of the same sex and similar age can be compared directly, because the formula already adjusts for height and weight.

ABSI is dimensionless but not weightless. A higher number means more central fat relative to the rest of the body, and a lower number means less. The Krakauer cohort used it to predict premature mortality risk, so the number is best read as a health risk summary, not a body image score.

If you want the mass-only number that this calculator is paired with, BMI Calculator reads the same height and weight and is the natural starting point for the comparison.

The calculator converts every input to metric, computes BMI, and then applies the Krakauer 2012 formula to produce ABSI. It then subtracts the sex-specific Krakauer reference mean and divides by the reference SD to produce a z-score, and finally uses the Krakauer mortality coefficient to translate the z-score into a hazard multiplier.

• WC (waist circumference): Waist in metres, measured at the narrowest part of the torso between the ribs and the iliac crest.
• BMI: Body mass index in kg per square metre, computed from the entered weight and height. Raising it to the two-thirds power scales it to a body-shape-relevant dimension.
• height (in metres): Standing height in metres, raised to the one-half power so that waist scales correctly for tall and short adults.
• mean_sex and SD_sex: Sex-specific Krakauer 2012 reference values: mean 0.0807 and SD 0.0053 for men, mean 0.0779 and SD 0.0050 for women.
• 0.0839: Krakauer mortality coefficient per one-standard-deviation rise in ABSI z-score in the reference cohort.

The two exponents are not arbitrary. The two-thirds power on BMI and the one-half power on height were chosen so that ABSI scales with waist and is roughly uncorrelated with height, weight, and BMI in the Krakauer reference cohort. That property is what lets the index summarise body shape rather than body size.

According to Krakauer and Krakauer, PLOS ONE 2012, ABSI is computed as waist circumference divided by BMI to the two-thirds power times the square root of height, and a one-standard-deviation rise in the index was associated with a mortality hazard ratio of about 1.09 in the reference cohort

If you want a one-number waist summary that does not use height or weight, Waist to Hip Ratio Calculator produces a single ratio that pairs naturally with ABSI as a different perspective on the same waist tape.

Four short definitions keep ABSI honest. They are the same terms the Krakauer papers use, and they show up in any serious discussion of body-shape statistics.

These four ideas produce the three numbers the calculator reports. The band is the headline, the z-score is the audit trail, and the hazard multiplier is what to compare against BMI when the reader wants a different lens on the same waist measurement.

ABSI is a shape summary, not a body composition number, and Body Fat Calculator turns the same height and weight into a body fat percentage that can be read alongside it.

Use a soft non-stretchable tape for waist, a stadiometer or a wall-and-book setup for height, and a calibrated scale for weight. Take the three measurements once, breathe out gently, and enter the numbers in the unit system you are using.

1. 1 Measure waist circumference: Wrap the tape at the narrowest part of the torso, between the ribs and the iliac crest. The tape should sit flat, parallel to the floor, and not compress the skin.
2. 2 Measure height: Stand against a wall without shoes, heels together, and read the top of the head. A clinic stadiometer reading is good enough if you do not have a wall setup.
3. 3 Measure weight: Weigh yourself in light clothing on a calibrated scale, ideally at the same time of day each visit.
4. 4 Pick a unit system and a reference sex: Choose metric or imperial, then pick the reference sex used for the Krakauer z-score.
5. 5 Read the band, the z-score, and the hazard multiplier: Start with the band in plain language, then read the z-score and the hazard multiplier together. A higher or much higher band is a prompt to talk to a clinician, not a diagnosis.

Worked walkthrough. A reader measures 80 cm waist, 165 cm height, 65 kg weight, female, age 30, in metric. The calculator reads BMI 23.9, ABSI 0.0751, z-score -0.56, hazard 0.95, and labels the result similar to reference. The same reader switching to imperial with 31.5 in, 65 in, 143.3 lb gets the same result within rounding.

If the band says you are above reference and you want a target range to work toward, Ideal Body Weight Calculator reads the same height and sex and gives a starting weight window rather than a single number.

A short list of what the calculator does well, and what it is not designed to do, helps the reader place the result in the right context.

Treat the band as a screening signal, not a verdict. The Krakauer cohort is large and population-level, so the band describes a population, not an individual outcome. Persistent concerns about central adiposity belong with a clinician.

If the band is higher than reference and you want to plan a calorie target, TDEE Calculator reads the same height, weight, age, and sex to estimate daily energy expenditure as a starting point.

Some factors change the number, some only change the context, and some the calculator cannot see at all.

• • The calculator is a screening tool, not a medical assessment. A higher-than-reference band is a prompt to talk to a clinician, especially with a family history of cardiovascular disease or diabetes.
• • The Krakauer 2012 reference is a US adult cohort, so ABSI may be less accurate in adults of different genetic backgrounds, very high muscle mass, or pregnancy. Pregnant readers and adolescents should not treat it as a health verdict.

The band and the hazard multiplier come from the same published reference. A reader whose ABSI is much higher than reference has a higher mortality hazard in the Krakauer cohort, not necessarily in their own life; the band is best used as a prompt, not a forecast.

According to Krakauer and Krakauer, Journal of Obesity 2015, the sex-specific ABSI z-score is a stable summary of body shape and tracks premature mortality in cohorts beyond the original 2012 study

If a much-lower-than-reference result has you wondering whether a small frame is part of the picture, Body Frame Size Calculator reads height and wrist to label the frame as small, medium, or large and pairs naturally with the index.