Body fat is calculated through several methods such as hydrostatic weighing, bioelectrical impedance, and skin fold calipers.
Hydrostatic weighing requires a specialized location with access to a pool designed for this type of measurement. An individual is submerged into the pool and weighed; they are then the weighed on dry land. Since lean body mass is more dense, it will sink and the fat will float. The difference in the dry and wet weight is calculated to determine the amount of body fat the individual has. This is the most accurate form of measuring body fat.
Bioelectrical impedance works by sending a low voltage electrical current through the body to measure fat. Since muscles are composed of a high percentage of water (which is a conductor of electricity) the current will pass through at a higher rate. This yields the percentage of body fat. Due to the electrical current, the accuracy of this method can be affected by levels of hydration.
The skin fold method is a very common method of calculating body fat. This test estimates the percentage of body fat by using a caliper to measure the skin fold thickness at specific points on the body. The Durnin-Womersley formula is commonly used to calculate body fat. This formula uses four specific spots on the body for the calculation. These spots are the front of the upper arm (biceps), back of the upper arm (triceps), below the shoulder blade (subscapular), and just above the hipbone (iliac crest). The results of each measurement are added together and the sum is found on a Durnin-Womersley body fat percentage calculation table under the appropriate category and recorded. Although there is some error associated with this method, finding a skilled professional to perform it increases the accuracy.