The YMCA uses a simple equation to estimate the body fat in adults.
 

Parameters

(1) waist circumference at the level of the umbilicus (navel) in inches
(2) weight in pounds
(3) gender
 

Formulae

(1) male body fat in pounds = (4.15 * (waist circumference in inches)) - (0.082 * (body weight in pounds)) - 98.42

(2) female body fat in pounds = (4.15 * (waist circumference in inches)) - (0.082 * (body weight in pounds)) - 76.76

(3) percent body fat = (body fat in pounds) / (body weight in pounds)