This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
What the body adiposity index is
The body adiposity index (BAI) estimates body fat percentage from two tape-measure values: hip circumference and height. Richard Bergman and colleagues published it in 2011 as an alternative to BMI that does not need a scale and gives a body fat percentage directly.
The formula
BAI = hip circumference (cm) ÷ height (m)^1.5 − 18
Measure the hips at the widest point of the buttocks, standing, with the tape horizontal and snug but not compressing the skin. The calculator converts inches to centimeters for you.
Example
A woman 5 ft 4 in tall (1.63 m) with 40 in hips (101.6 cm): 1.6256^1.5 = 2.073, and 101.6 ÷ 2.073 − 18 = 31.0% estimated body fat. If she weighs 150 lb, that is about 46.5 lb of fat and 103.5 lb of lean mass.
Reference ranges
Bergman’s group proposed ranges by sex and age. For adults aged 20 to 39:
| Category | Women | Men |
|---|---|---|
| Underweight | under 21% | under 8% |
| Healthy | 21 to 33% | 8 to 21% |
| Overweight | 33 to 39% | 21 to 26% |
| Obese | over 39% | over 26% |
The healthy ranges shift up by about one to three points for people aged 40 to 59 and again after 60.
How accurate is it?
The BAI was developed in Mexican-American adults and validated against DXA scans in African-American adults. Later studies found it:
- Tends to overestimate body fat in lean people and men.
- Tends to underestimate it in people with a lot of body fat.
- Is not more accurate than BMI for predicting health risks on average.
Its main advantage is practical: it needs only a tape measure, and it reports fat percentage rather than a weight-for-height number.
Better ways to track body fat
For a single reading, a DXA scan is the reference method. For tracking change over time at home, use the same tape measurements, the same time of day and the same conditions every time; the waist-to-height ratio adds information about belly fat, which is the most strongly linked to cardiovascular risk.