Body fat scales send a low, safe electrical current through the body to measure its composition. The electrical current passes more easily through lean muscle than it does through fat. Body composition is calculated mathematically, based upon the speed at which the signal passes through the body. This is how a body fat reading is determined. Body fat scales use a technique called Bioelectrical Impedance Analysis... or BIA for short. Like all body fat tests out there, these scales do not actually measure your body fat percentage. They determine your body density. The examiner (or the scales) then uses a formula to calculate body fat percentage based on body density. These formulas only predict your body fat. Unfortunately there is no one formula that accurately predicts body fat for the whole population. Differences in age, gender, ethnicity, body size, and fitness level all have a significant affect on the results, and are important factors that make body fat indexes differ.

Tanita makes a popular array of body fat scales. The TBF-511 and TBF-515 models use the same revolutionary method of measuring bio electrical impedance analysis (BIA) that give a fast, less intrusive, safe, and accurate way of measuring a person's body fat. It's as simple to use a body fat scale as it is to step on a traditional scale. Just step on; these scales give an accurate reading of both weight and body fat within 30 seconds.

Body fat scales also come with a wide array of extra features. Some include memory for up to 4 users, and others have a "guest mode" available for irregular users. Some can measure bone mass, body fat percentage and total body water weight. According to some scale manufacturers, fat readings can vary, depending on whether you've just exercised, eaten, or even showered.