Bioimpedance Body Fat Estimate Calculator

About this calculator

Bioelectrical Impedance Analysis (BIA) estimates body composition by sending a tiny, imperceptible electrical current through the body and measuring how much it is impeded. That impedance breaks down into two components: resistance, the opposition to current flow through the body's water and electrolytes (lean tissue, which holds more water, conducts better and shows lower resistance than fat), and reactance, the delay caused by cell membranes acting like tiny capacitors, which reflects cell membrane health and integrity.

Using your height, weight, sex, and these resistance and reactance readings, regression equations (built from BIA validation research against reference methods like DEXA and hydrostatic weighing) estimate your fat-free mass (FFM); subtracting FFM from total body weight then gives your estimated body fat mass and percentage.

This is the same underlying technology used in home smart scales, handheld body-fat analyzers, and clinical devices, and it is popular precisely because it's fast and non-invasive, though results can shift with hydration status, recent exercise, or meals — clinicians also use raw resistance/reactance readings (via phase angle) as a marker of nutritional and fluid status in conditions like dialysis.