Body Adiposity Index (BAI) Calculator
Estimate body fat percent from hip circumference and height using the BAI formula.
An alternative to BMI that uses only a tape measure — no scale needed.
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 — useful in field studies, large epidemiological surveys, and remote populations.
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 = 2.218
- BAI = (95 / 2.218) − 18 = 42.83 − 18 = 24.8%
That puts this person near the upper-normal range for a young adult.
BAI Interpretation Bands (Bergman et al., 2011)
| 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 |
In population studies, BAI correlates well with DXA-measured body fat in both men and women, but it tends to underestimate fat in muscular individuals and overestimate it in those with broad pelvic structure.
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.