The Body Fat Percentage (BFP) is a measure of fitness level, calculated by dividing the total mass of fat divided by total body mass. Body fat includes essential body (necessary to maintain life and reproductive functions) fat and storage body fat (which consists of fat accumulation in adipose tissue). It must be noted that the percentage of essential body fat for women is greater than that for men, due to the demands of childbearing and other hormonal functions. They are several methods you can use to estimate (since measuring requires sophisticated equipment) the percentage of body fat: RFM: the Relative Fat Mass index is a method developed by investigators from the Cedars-Sinai Medical Center, who examined more than 300 possible formulas for estimating body fat, using a database of 12,000 adults, and then confirmed their results by measuring the fat percentage of 3,500 patients. US Navy: is an equation developed at the Naval Health Research Center by Hodgdon and Beckett in 1984, and currently used by the US Navy on their service members. Deurenberg: is a revision of the Body Mass Index formula, which adds coefficients for the age and sex. Isn't very accurate and should be used only as a orientative value. Please note that these methods were developed to be applied on middle aged people. You should consult your physician for guidelines that fit you.