Most body fat formulas need at least a scale and often several tape measurements. The body adiposity index, or BAI, takes a different approach: it uses only the circumference of the hips and the person’s height. Richard Bergman and colleagues proposed it in 2011 after finding that hip size, scaled to height, tracked the percentage of body fat measured by DXA in a large group of Mexican American and African American adults. The appeal is clear: no weight is required, and the hip is an easy place to measure. This calculator applies the equation and, as importantly, explains where it falls short.
Think of the result as a rough estimate to compare with other methods, not as a measurement.
How to use the body adiposity index calculator
- Measure your hips around the widest part of the buttocks, standing with feet together, with the tape level.
- Measure your height without shoes.
- Enter both, in any units, and choose sex if you want the descriptive category.
- Read the estimate and compare it with a second method.
BAI formula
The equation is from Bergman RN, Stefanovski D, Buchanan TA, et al., A better index of body adiposity, Obesity (Silver Spring) 2011;19:1083–1089. The power of 1.5 on height was chosen so that the index did not depend on stature, and the constant 18 makes the result comparable with percent body fat.
Worked example
A woman with 100 cm hips who is 170 cm tall.
- Height1.5 = 1.701.5 = 2.2165
- BAI = 100 ÷ 2.2165 − 18 = 45.12 − 18 = 27.1%
- On the ACE ranges for women that is in the average category.
BAI for sample hip sizes and heights
| Height | Hip 85 cm | Hip 95 cm | Hip 105 cm | Hip 115 cm |
|---|---|---|---|---|
| 155 cm | 26.0% | 31.2% | 36.4% | 41.6% |
| 165 cm | 22.1% | 26.8% | 31.5% | 36.3% |
| 175 cm | 18.7% | 23.0% | 27.4% | 31.7% |
| 185 cm | 15.8% | 19.8% | 23.7% | 27.7% |
Body fat categories
| Category (ACE) | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% and above | 32% and above |
The American Council on Exercise ranges are descriptive guides for adults and not clinical thresholds.
Limits of the body adiposity index
- Hip only. It ignores waist and abdominal fat, which carry more health risk than hip fat. A person with a large waist and slim hips can look lean on BAI.
- Population-specific. It was developed in two ethnic groups. Evaluations in European, Asian and other groups have found weaker agreement with DXA.
- No sex term. Women generally carry more fat at the same hip size, so the equation may be biased by sex.
- No better than BMI in many studies. It should not be used for diagnosis or to track small changes.
Better options
If you want a tape-based estimate, methods that include the waist have more support: the Navy circumference method (Navy Body Fat Calculator), relative fat mass (Relative Fat Mass (RFM) Calculator) and the YMCA formula (YMCA Body Fat Calculator). The Body Fat Calculator gathers several. Fat distribution can be checked with the Waist-to-Hip Ratio Calculator, and overall weight status with the BMI Calculator.
This page is for information only and is not medical advice. The body adiposity index is a research estimate with known limits; speak to a doctor about your own health.
Sources
- Bergman RN, Stefanovski D, Buchanan TA, et al. A better index of body adiposity. Obesity 2011;19:1083–1089.
- American Council on Exercise. What Are the Guidelines for Percentage of Body Fat Loss? (body fat categories).
Frequently asked questions
What is the body adiposity index?
The body adiposity index (BAI) is an equation proposed in 2011 by Richard Bergman and colleagues to estimate body fat percentage from hip circumference and height, without needing body weight. It was meant to be a practical alternative to BMI.
How accurate is BAI?
The original study, in Mexican American and African American adults, found BAI correlated well with body fat measured by DXA. Independent evaluations in other populations have generally found it no more accurate than BMI, and it tends to over- or under-estimate at the extremes. Treat it as a rough estimate.
Why does it use hip circumference?
Hip size reflects the amount of gluteal and femoral fat and the underlying bone structure, and the authors found it correlated with total body fat. It ignores abdominal fat, which carries more health risk, so combine it with a waist measurement.
Does sex matter?
The BAI equation itself has no sex term. The category shown here uses sex-specific ACE ranges for context only, so interpret the result with caution, particularly for men.
What should I use instead?
For tape measurements the US Navy method (see the Navy Body Fat Calculator) and relative fat mass (Relative Fat Mass (RFM) Calculator) use the waist as well and have more evidence. A DEXA scan is the standard for an accurate figure.