Body Adiposity Index
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BAI estimates body fat percentage using hip circumference and height only, without requiring body weight, unlike BMI which uses weight and height. It was developed as an alternative that some researchers believed might better estimate body fat than BMI, particularly across different ethnic groups.

The formula's developers aimed to create a measure that didn't require a scale, using hip circumference as a proxy correlated with body fat instead. This makes BAI potentially more convenient in settings without access to accurate scales, though it introduces its own sources of estimation error.

Results have been mixed; several validation studies found BAI didn't consistently outperform BMI for estimating body fat percentage across diverse populations, and in some studies performed worse. It hasn't replaced BMI as the dominant screening tool despite its original promise.

Like BMI, BAI can't distinguish muscle mass from fat mass, so a muscular individual with a larger hip circumference from muscle rather than fat could show an inflated body fat estimate. Neither BAI nor BMI substitute for direct body composition measurement methods like DEXA.

Either can be tracked consistently over time as a rough trend indicator, but neither precisely measures body fat, so significant lifestyle or training changes are better monitored with more direct methods like skinfold calipers, bioelectrical impedance, or DEXA scanning when available.