Body Density Calculator - Measure Body Fat Using Hydrostatic Weighing

Hydrostatic weighing, also known as underwater weighing, is a method using the Archimedes principle which states that when a body is submerged in water, there is a buoyant counter force equal to the weight of the water which is displaced. Because bone and muscle are more dense than water, a person with a larger percentage of fat free mass will weigh more in the water and have a lower percent body fat. Conversely, fat floats. Therefore, a large amount of fat mass will make the body lighter in the water and have a higher percent body fat.

How Accurate Is Hydrostatic Weighing?
If each test is performed correctly according to the recommended guidelines, there is a +/- 1.5% error. (Note: Accuracy depends on the client’s ability to blow all the air out of their lungs both during a pre-test screening with a spirometer, and during the test itself. Since air makes the body float, inability to perform either of these maneuvers will result in miscalculation of the percent body fat).

Hydrostatic weighing is currently considered the "gold standard" in measuring body fat percentage. Repeat measures using underwater weighing usually prove consistent and can be used to chart progress.