What Is an ABSI Calculator?
A Body Shape Index, or ABSI, is a body measurement developed by Nir and Jesse Krakauer in 2012 to fix a specific gap in BMI. BMI uses weight and height but ignores where you carry fat. Two people with identical BMI can have very different health outcomes because one stores fat around the waist and the other stores it under the skin on the hips. ABSI isolates the effect of abdominal size by asking a simple question: given your height and weight, how much bigger is your waist than expected?
The ABSI calculator takes your sex, age, height, weight, and waist circumference, computes your ABSI, and converts it to a z-score that compares you to people of the same age and sex. A positive z-score means your waist is larger than average for your build. The original Krakauer study, published in PLoS ONE, used data from over 14,000 adults in NHANES and found that ABSI predicted premature mortality more strongly than either BMI or waist circumference alone. Each one standard deviation increase in ABSI was associated with roughly a 14% higher death risk over the follow-up period, even after adjusting for BMI, smoking, and other factors.
How the Calculation Works
The formula has two parts. First, BMI is calculated in the usual way:
BMI = weight (kg) / height (m)²
Then ABSI is computed as:
ABSI = waist (cm) / (BMI^(2/3) × height (m)^(1/2))
The exponents are the key. By dividing waist by BMI raised to the two-thirds power, the formula strips out the waist size that is explained by overall body size. What remains is a measure of how much your waist sticks out beyond what your weight and height would predict. A taller, heavier person naturally has a larger waist. ABSI corrects for that, so the number reflects concentrated abdominal fat rather than just being big.
The raw ABSI value is hard to interpret on its own because it is a small number, typically between 0.075 and 0.090 for adults. That is why the calculator converts it to a z-score using population reference data:
z-score = (your ABSI - population mean ABSI) / population SD
The reference mean and standard deviation depend on your age and sex, because ABSI drifts upward with age and differs between men and women. A z-score of 0 means your ABSI is exactly average for your group. A z-score of +1 means it is one standard deviation above average.
Risk Categories by z-Score
| z-Score Range | Category | Interpretation |
|---|---|---|
| Below -0.87 | Lowest risk | Well below average abdominal size |
| -0.87 to +0.34 | Below average risk | Smaller than typical waist for build |
| +0.35 to +1.08 | Average risk | Close to population average |
| +1.09 to +1.79 | Above average risk | Larger than expected waist |
| +1.80 and above | Highest risk | Substantially elevated mortality risk |
The boundaries correspond to population quintiles from the original NHANES analysis. People in the highest ABSI quintile had a death rate more than double that of the lowest quintile over the study period.
How to Use the Calculator
- Select your sex. ABSI reference values differ for men and women.
- Choose imperial or metric units.
- Enter your age. The reference mean ABSI rises with age, so this changes your z-score.
- Enter your height and weight. These feed the BMI part of the formula.
- Enter your waist circumference at the narrowest point, just above the belly button, after a normal exhale.
- Your ABSI, z-score, risk category, and relative mortality risk appear on the right.
Example Calculations
Example 1: Two Men with the Same BMI
Mark and James are both 45-year-old men, 5 foot 10 (178 cm) and 190 pounds (86 kg). Their BMI is identical at 27.1. But Mark has a 36 inch (91 cm) waist and James has a 42 inch (107 cm) waist.
- Mark: ABSI = 91 / (27.1^(2/3) × 1.78^(1/2)) = 0.0806. Reference mean for men 40-49 is 0.0810. z = (0.0806 - 0.0810) / 0.0052 = -0.08. Average risk.
- James: ABSI = 107 / (27.1^(2/3) × 1.78^(1/2)) = 0.0948. z = (0.0948 - 0.0810) / 0.0052 = +2.65. Highest risk.
- Takeaway: BMI said both men were equally healthy. ABSI shows James carries dangerous abdominal fat that roughly triples his estimated mortality risk relative to Mark.
Example 2: Older Woman Tracking Her Ratio
Helen is 68, 5 foot 4 (163 cm), 150 pounds (68 kg), with a 37 inch (94 cm) waist. Her BMI is 25.6, just over the healthy line. Her ABSI is 94 / (25.6^(2/3) × 1.63^(1/2)) = 0.0854. The reference mean for women 60-69 is 0.0820 with SD 0.0056. Her z-score is (0.0854 - 0.0820) / 0.0056 = +0.61, which is average risk. She also checks her waist-to-height ratio of 0.58, which flags moderate risk. The two metrics agree she has some abdominal fat to lose but is not in the danger zone.
Real-World Scenarios
The TOFI Patient
Daniel is 33, 6 foot 1 (185 cm), and 172 pounds (78 kg). His BMI is 22.8, normal. But he works long hours at a desk, eats takeout, and his waist has crept up to 39 inches (99 cm). His ABSI is 99 / (22.8^(2/3) × 1.85^(1/2)) = 0.0879. The reference mean for men 30-39 is 0.0800, SD 0.0050. His z-score is +1.58, above average risk. His doctor ordered a fasting insulin test, which came back elevated at 14 uIU/mL. This is the TOFI pattern, thin outside, fat inside. Visceral fat around the organs drives insulin resistance even at a normal BMI. Daniel started walking 45 minutes a day and reduced his waist to 35 inches over five months, dropping his z-score to +0.78.
Reassessing After Weight Loss
Sofia, 52, started at 210 pounds (95 kg), 5 foot 5 (165 cm), with a 44 inch (112 cm) waist. Her ABSI z-score was +2.10, highest risk. Over a year she lost 35 pounds through a calorie deficit and strength training. Her waist dropped to 36 inches (91 cm). Recalculating, her ABSI is 91 / (26.4^(2/3) × 1.65^(1/2)) = 0.0839, z-score +0.64, average risk. Notice her BMI is still 26.4, technically overweight, but her ABSI normalized because she lost the visceral fat that mattered most. She used our BMI Calculator alongside ABSI to see the full picture, and the contrast showed why BMI alone can be misleading during weight loss.
The Athletic Build
Marcus is a 28-year-old powerlifter, 5 foot 9 (175 cm), 205 pounds (93 kg), with a 36 inch (91 cm) waist. His BMI is 30.4, obese. His ABSI is 91 / (30.4^(2/3) × 1.75^(1/2)) = 0.0776. The reference mean for men 18-29 is 0.0790, SD 0.0048. His z-score is -0.29, below average risk. ABSI correctly identifies that his waist is not large for his size, because his weight is muscle, not visceral fat. This is a case where ABSI outperforms BMI, which would wrongly label him obese. He still tracks his body fat percentage to confirm the muscle-to-fat ratio.
Common Mistakes to Avoid
- Comparing raw ABSI across people: Raw ABSI values are small and unintuitive. Always use the z-score, which accounts for age and sex. A raw ABSI of 0.083 is average for a 65-year-old man but high for a 25-year-old man.
- Measuring waist inconsistently: ABSI is sensitive to waist measurement because it is the numerator. A 2 inch error shifts your z-score by roughly half a standard deviation. Measure at the narrowest point, above the belly button, after a normal exhale, with the tape parallel to the floor.
- Treating ABSI as a diagnosis: ABSI estimates population-level mortality risk from a single body measurement. It does not detect disease, measure visceral fat directly, or replace a clinical workup. A high z-score is a prompt to talk to a clinician, not a verdict.
- Forgetting that the reference data is population-based: The reference mean and SD come from NHANES, a US population sample. People from some ethnic backgrounds may have different typical ABSI distributions. The z-score is most meaningful when compared against a relevant population.
- Ignoring other risk factors: ABSI captures abdominal size, but smoking, blood pressure, cholesterol, family history, and activity level all matter. A low ABSI does not cancel out a smoking habit. Use ABSI as one input among several.
Authoritative Research and Resources
- Krakauer NY, Krakauer JC. A new body shape index predicts mortality hazard independently of BMI (2012, PLoS ONE) - The original study that developed ABSI from NHANES data and showed it predicted premature mortality more strongly than BMI or waist circumference, with each standard deviation increase raising death risk by about 14%.
- CDC National Health and Nutrition Examination Survey (NHANES) - The nationally representative survey data used to derive the ABSI reference values and validate the metric against mortality outcomes.
- AHA 2026 Dietary Guidance to Improve Cardiovascular Health (Circulation) - The American Heart Association's 2026 scientific statement linking abdominal adiposity to cardiovascular risk and recommending dietary patterns that minimize added sugars and ultraprocessed foods.