A body fat scale is designed to estimate a person's body fat percentage. It uses a technology called bioelectrical impedance analysis (BIA) to measure the resistance of electrical current as it travels through the body. To use a body fat scale, the user typically stands on the scale with bare feet and holds onto metal electrodes on the scale's handlebar. The scale then sends a low-level electrical current through the body, which travels more easily through muscle than through fat. By measuring the resistance of the current, the scale can estimate the amount of body fat a person has.