The calculation was put forth by Bergman et al.:
A Better Index of Body Adiposity, Nature: Obesity, March 2011
BAI = (hip circumference in centimeters / height in meters1.5) − 18
It supposedly correlates well with dual-energy X-ray absorptiometry (DXA). DXA actually measures body fat indirectly but is considered comparable to hydrostatic or underwater weighing.
Examples using BAI calculation:
- A man with hips of 42" and height of 5'10" would have a body fat of about 27%.
- A woman with hips of 36" and height of 5'4" would have a body fat of about 26%.
You can calculate your own BAI or body fat percentage here: Texas State University BAI Body Fat Calculator
None of these metrics (BMI, BAI, etc.) give an accurate measure of body composition, but taken together they give a better indication of health than any single measure:
The Body Adiposity Index (Hip Circumference ÷ Height1.5) Is Not A More Accurate Measure Of Adiposity Than Is BMI, Waist Circumference, Or Hip Circumference, Nature: Obesity, April 2012
The image at the top is from Wikipedia: Waist-Hip Ratio. I thought it offered a good reference for where to measure hips.