ABSI Calculator

Estimate ABSI, BMI, waist-to-height ratio, and relative central-adiposity risk from waist, height, weight, age, and sex.

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Formula

ABSI = WC / (BMI^(2/3) x Height^(1/2))

WC is waist circumference in meters, BMI is body mass index in kg/m2, and Height is in meters. The formula normalizes waist circumference relative to what is expected for a given BMI and height. The result is converted to a z-score using age and gender-specific population reference values. Each standard deviation increase is associated with approximately 13% higher mortality risk.

Worked Examples

Example 1: Average Risk Male Assessment

Problem: A 40-year-old male, 5 ft 10 in (1.778m), 170 lbs (77.1 kg), 34-inch (86.4 cm) waist.

Solution: BMI: 77.1 / 1.778^2 = 24.4\nABSI: 0.864m / (24.4^(2/3) x 1.778^(1/2))\n= 0.864 / (8.41 x 1.333)\n= 0.864 / 11.21\n= 0.0771\nPopulation mean (male, age 40): 0.0790\nSD: 0.0042\nZ-score: (0.0771 - 0.0790) / 0.0042 = -0.45\nRelative risk: e^(0.13 x -0.45) = 0.94

Result: ABSI: 0.0771 | Z-score: -0.45 | Low Risk | Relative Risk: 0.94x

Example 2: Elevated Risk Female Assessment

Problem: A 55-year-old female, 5 ft 4 in (1.626m), 180 lbs (81.6 kg), 38-inch (96.5 cm) waist.

Solution: BMI: 81.6 / 1.626^2 = 30.9\nABSI: 0.965m / (30.9^(2/3) x 1.626^(1/2))\n= 0.965 / (9.87 x 1.275)\n= 0.965 / 12.58\n= 0.0767 (note: raw value can be lower with high BMI)\nPopulation mean (female, age 55): 0.0798\nSD: 0.0044\nZ-score varies by exact reference\nElevated waist-to-height ratio: 0.594

Result: ABSI assessment with elevated waist-to-height ratio indicating central adiposity risk

Example 3: Krakauer & Krakauer - A New Body Shape Index Predicts Mortality (PLoS One 2012)

Problem: A middle-aged adult wants to know whether waist size looks elevated after height and BMI are considered too.

Solution: Enter waist, height, weight, age, and sex. The calculator returns ABSI, a z-score estimate, BMI, and waist-to-height ratio so the result is easier to interpret in context.

Result: A near-average ABSI suggests waist size is broadly in line with the person overall body size.

Frequently Asked Questions

What is ABSI and what does it measure?

ABSI stands for A Body Shape Index, a metric developed by Dr. Nir and Jesse Krakauer in 2012 to assess mortality risk based on body shape independent of BMI. Unlike BMI which only considers height and weight, ABSI incorporates waist circumference to evaluate how your body fat is distributed. Central obesity, characterized by excess fat around the midsection, is strongly associated with increased risk of cardiovascular disease, type 2 diabetes, and premature death. ABSI essentially measures whether your waist circumference is larger or smaller than expected for your height and BMI. A higher ABSI indicates a more centrally obese body shape and elevated health risk.

How is ABSI calculated and what is the formula?

ABSI is calculated using the formula: ABSI = WC divided by (BMI raised to the power of two-thirds multiplied by height raised to the power of one-half), where WC is waist circumference in meters and height is in meters. The formula normalizes waist circumference against what would be expected for a given BMI and height, isolating the effect of body shape from overall body size. The resulting value is a small number typically around 0.07 to 0.09. This raw value is then converted to a z-score by comparing it to age and gender-specific population averages. Each standard deviation increase in ABSI above the mean is associated with approximately 13 percent higher premature mortality risk.

How does ABSI compare to BMI for predicting health risks?

ABSI provides complementary information to BMI and may be a better predictor of mortality risk in certain populations. BMI fails to distinguish between muscle mass and fat mass, and does not account for fat distribution. Two people with identical BMIs can have very different health risk profiles if one carries fat centrally while the other does not. Research published in PLoS One found that ABSI was a significant predictor of mortality even after adjusting for BMI, whereas BMI alone was a weaker predictor when ABSI was included. The combination of BMI and ABSI together provides a more comprehensive assessment of body composition-related health risk than either metric alone.

What is a normal ABSI value and what values indicate risk?

ABSI values are best interpreted through z-scores rather than raw numbers, as the raw value varies with age and gender. A z-score of zero means your ABSI exactly matches the population average for your age and gender. Values below negative 0.5 indicate lower than average risk, while values above 0.5 indicate higher than average risk. A z-score above 1.0 represents a meaningfully elevated mortality risk of approximately 13 percent or more above average. Values above 2.0 suggest very high risk. Population ABSI values typically range from 0.07 to 0.09 in raw units. The most important comparison is not the absolute number but where you fall relative to your age and gender peers.

How should waist circumference be measured for accurate ABSI calculation?

Accurate waist circumference measurement is critical for reliable ABSI calculation. Measure at the midpoint between the lowest palpable rib and the top of the iliac crest, which is the upper edge of the hip bone, in accordance with World Health Organization guidelines. Stand upright with feet together, arms at your sides, and measure at the end of a normal exhalation. Place the tape measure snugly but without compressing the skin. Do not measure over clothing. Take the measurement twice and use the average if there is a discrepancy. Measuring at the navel level is an acceptable alternative but may give slightly different results. Morning measurements are most consistent before eating or drinking.

Does ABSI change with age and does this affect interpretation?

ABSI tends to increase with age in both men and women, reflecting the natural tendency toward increased central fat storage with aging. The population mean ABSI increases approximately 0.0001 to 0.0002 units per year of age beyond 40. This is why ABSI z-scores are age-adjusted, comparing your value to others in your age group rather than the overall population. An ABSI value that would be average for a 60-year-old might be above average for a 30-year-old. The age-adjusted z-score accounts for these differences, making ABSI a fair comparison tool across the lifespan. However, a high ABSI z-score at any age warrants attention to waist circumference reduction strategies.