About the ABSI Calculator (A Body Shape Index)
A Body Shape Index (ABSI) was developed by Nir and Jesse Krakauer in 2012 to capture what BMI misses: whether your waist is large for your height and weight. It divides waist circumference by BMI to the power 2/3 and height to the power 1/2, which makes it almost uncorrelated with BMI itself. In their analysis of 14,105 US adults from NHANES 1999–2004, a higher ABSI predicted higher death rates even after accounting for BMI, smoking, diabetes, blood pressure and cholesterol.
Raw ABSI values are small numbers around 0.08 that rise with age, so on their own they are hard to interpret. This calculator converts your ABSI into a z-score using the age- and sex-specific means and standard deviations published with the original paper, then shows your percentile, risk quintile and the waist size that would give an average ABSI for your height and weight.
ABSI is a research and screening indicator, not a diagnosis. The reference values come from adults aged 18 to 85 in the US population, and the association with mortality was weaker for Mexican-American participants in the original study. Use it alongside BMI, waist-to-height ratio and medical advice.
With the default inputs, the absi is 0.0792 m^(11/6) kg^(−2/3). Change any value above to recalculate instantly.
How to use the absi calculator (a body shape index)
- 1Choose US or metric units and select your sex.
- 2Enter your age, height and weight.
- 3Measure your waist at the top of the hip bone after breathing out, and enter it.
- 4Read your ABSI, z-score, percentile and risk quintile.
- 5Use the "waist for an average ABSI" figure as a reference point for your build.
Formula and method
Waist circumference (WC) and height (H) are in metres and BMI is weight in kg divided by height in metres squared. The exponents were chosen by Krakauer and Krakauer so that ABSI is essentially independent of height, weight and BMI in the NHANES population; what is left reflects relative abdominal size.
Because ABSI rises with age and differs by sex, the z-score compares your value with the smoothed mean and standard deviation for your single year of age and sex from the paper’s supplementary Table S1 (ages 18–85+). The percentile assumes a normal distribution, and the risk group and hazard ratio use the quintile results reported in the paper (middle quintile = 1.00).
- WC
- Waist circumference (m)
- BMI
- Body mass index (kg/m²)
- H
- Height (m)
- z
- Standard deviations above or below the age-sex mean
Worked examples
45-year-old man, 5 ft 10 in, 185 lb, 37-inch waist
Height 1.778 m and 83.9 kg give a BMI of 26.5. The 0.9398 m waist divided by 26.5^(2/3) × 1.778^(1/2) gives ABSI ≈ 0.0792. The male mean at 45 is 0.08165 (SD 0.00368), so z ≈ −0.66, around the 25th percentile — the second quintile.
60-year-old woman, 165 cm, 70 kg, 98 cm waist (metric)
BMI is 70 ÷ 1.65² = 25.7. ABSI = 0.98 ÷ (25.7^(2/3) × 1.65^(1/2)) ≈ 0.0876. Against the female mean of 0.08105 (SD 0.00509) at 60, z ≈ 1.28, about the 90th percentile — the top quintile, where the paper found 1.93 times the hazard of the middle fifth.
30-year-old man, 6 ft 0 in, 200 lb, 42-inch waist
A 1.8288 m man weighing 90.7 kg has a BMI of 27.1. His 1.0668 m waist gives ABSI ≈ 0.0874, far above the age-30 male mean of 0.07951 (SD 0.00374): z ≈ 2.1, around the 98th percentile.
Frequently asked questions
What is a normal ABSI?+
Raw ABSI in adults is usually between about 0.07 and 0.09 and rises with age. Because of that, it is best read as a z-score: 0 is average for your age and sex, negative is below average and positive values indicate a relatively larger waist.
Is ABSI better than BMI?+
They measure different things. BMI reflects overall size, while ABSI reflects waist size relative to height and weight. In NHANES data, ABSI predicted mortality independently of BMI, so using both gives a fuller picture than either alone.
What ABSI z-score is high risk?+
In the original study, death rates rose roughly exponentially above average ABSI. The top fifth of the population (about z above 0.84) had about 1.9 times the hazard of the middle fifth, and each 1-SD increase added roughly 33% risk.
Where should I measure my waist for ABSI?+
The reference data come from NHANES, which measures waist circumference just above the top of the hip bone (iliac crest) at the end of a normal breath out. Using a different site may shift your result slightly.
Can I lower my ABSI?+
Yes. Losing abdominal fat reduces waist size faster than overall weight, lowering ABSI. Regular physical activity, especially combined aerobic and resistance training, and an overall healthy diet are the main approaches.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.