Body Adiposity Index (BAI) Calculator
Estimate body fat percent from hip circumference and height using the BAI formula.
A BMI alternative needing only a tape measure, with age and sex bands.
Body Adiposity Index (BAI)
The Body Adiposity Index, proposed by Bergman and colleagues in 2011, estimates body fat percentage from just two tape-measure inputs: hip circumference and height. Because no weight is needed, BAI can be measured anywhere. That was the point of it: field studies, large epidemiological surveys and remote populations where a calibrated scale is a problem but a tape measure is not.
Formula
BAI = (hip circumference in cm / (height in m)^1.5) − 18
Result is read directly as a percent.
Worked Example
A person with a hip circumference of 95 cm and height of 1.70 m:
- (1.70)^1.5 = 1.70 × √1.70 = 1.70 × 1.3038 = 2.2165
- BAI = (95 / 2.2165) − 18 = 42.86 − 18 = 24.9%
What that means depends entirely on who the person is, which is the part most BAI write-ups skip. For a woman in her thirties, 24.9% sits in the lower half of the healthy band and needs no comment. For a man of the same age it is overweight, because the male healthy band tops out at 21%. Same tape measure, same two numbers, opposite verdicts. Always read BAI against the row for your own sex and age.
Interpretation Bands
A note on where these come from, because it is widely misreported. The Bergman paper derived and validated the formula; it did not publish classification cutoffs. The bands below are the age- and sex-specific body-fat-percentage ranges from Gallagher and colleagues (American Journal of Clinical Nutrition, 2000), which is what BAI results are normally read against, since BAI is expressed as a body fat percentage.
| Age | Underweight | Healthy | Overweight | Obese |
|---|---|---|---|---|
| Women, 20–39 | < 21% | 21–33% | 33–39% | > 39% |
| Women, 40–59 | < 23% | 23–35% | 35–41% | > 41% |
| Women, 60–79 | < 25% | 25–38% | 38–43% | > 43% |
| Men, 20–39 | < 8% | 8–21% | 21–26% | > 26% |
| Men, 40–59 | < 11% | 11–23% | 23–29% | > 29% |
| Men, 60–79 | < 13% | 13–25% | 25–31% | > 31% |
BAI vs BMI
| Metric | Inputs Needed | Strengths | Weaknesses |
|---|---|---|---|
| BMI | Weight + height | Universally accepted | Cannot distinguish muscle from fat |
| BAI | Hip + height | No scale required | Less validated in athletes and certain ethnic groups |
| Body fat % (DXA) | Lab scan | Gold standard | Expensive |
Does BAI actually beat BMI?
Mostly no, and it is worth being straight about that on a page whose whole job is to compute it. The original 2011 paper reported a strong correlation with DXA in the Mexican-American and African-American cohorts it was developed on. The independent replications that followed were much less kind. Several large validation studies, including work by Freedman and colleagues in 2012, found BAI’s error against DXA was no better than plain BMI’s and often worse, with a pronounced sex bias: it tends to overestimate body fat in men and underestimate it in very muscular people of either sex. Hip circumference is doing the heavy lifting in the formula, and hips carry a different fraction of total fat in men than in women.
So where does that leave it? BAI earns its place when a scale is genuinely unavailable, or when you want a fat estimate that does not move when a lifter adds ten pounds of muscle. As a general-purpose replacement for BMI it has not held up, and the honest summary is that it is an interesting idea that did not replicate.
How to Measure Hip Circumference
Measure horizontally around the largest part of the buttocks while standing relaxed. Keep the tape level and snug but not compressing the tissue. Average two or three readings for accuracy.
Caveats
BAI is a statistical estimate, not a direct measurement. Individual results can vary by ±5% body fat from a clinical body-fat scan. Use BAI to track trends over time rather than as a single diagnostic number. For medical or training decisions, supplement BAI with at least one of: skinfold calipers, bioimpedance, or DXA.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.