Last updated: 2026-07-08

Body Adiposity Index

The Body Adiposity Index (BAI) estimates whole-body fat percentage from two measurements alone: hip circumference and height. It was introduced by Richard Bergman and colleagues in 2011 as a way to gauge body fat without a scale, since neither weight nor body mass index is part of the calculation. The figure it returns is read directly as an approximate percentage of body fat — a result of 27, for instance, suggests body fat of around 27 percent.

What the index represents

The index rests on the observation that hip circumference, scaled by height, correlates with the proportion of fat a body carries. A wider hip measurement relative to height points to greater adiposity, while a narrower one points to less. Because only a tape measure is required, the index suits settings where weighing is impractical, and it gives a number on the same scale that body-fat measurements use.

The formula

Here $\mathrm{HC}$ is the hip circumference in centimetres and $h$ is height in metres. The hip measurement is divided by height raised to the power of one and a half, and the constant of eighteen is then subtracted to bring the output onto the body-fat-percentage scale. No weight term appears anywhere in the expression.

Worked example

Consider an adult with a hip circumference of 100 cm39 in and a height of 1.70 m5 ft 7 in:

The result of about 27.1 is read as an estimated body fat of roughly 27 percent. Whether that figure is high, typical, or low depends on the person's sex and age.

Interpreting the number

There is no single universal cut-off for the index, because healthy body-fat ranges are specific to sex and age. Women carry more essential fat than men, so a value that is healthy for a woman can sit above the typical range for a man, and reference ranges shift upward with age in both. The number is therefore best read against a sex- and age-appropriate range rather than a fixed target. For an individual, the trend across several measurements usually says more than one reading on its own.

Limits

The index is an estimate built from a single circumference and height, so it cannot account for muscle, frame, or where fat is stored. Validation studies have found it tracks measured body fat reasonably well for many women but is less reliable for men and at the high and low extremes of body fat. It works best as an alternative entry point rather than a replacement for more direct methods: the Body Fat % Calculator (Navy Method) uses skinfold or girth-based equations, while BMI Calculator and the Waist-to-Hip Ratio Calculator describe different aspects of body composition. Any health decision should rest on a professional assessment rather than a single index.