My preferred choice for measuring body composition is Underwater weighing or Hydrostatic Weighing . I chose this as it is the most accurate among all the methods and is relatively cheap .
Hydrostatic Weighing is based upon 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 . As bones and muscles are more dense than water, a person with a lower percentage of fat 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.
With Hydrostatic Weighing , there is only a chance of +/- 1.5% error . However , it depends on the client's ability to blow all air out of their lungs during the pretest and the actual test . This is important as having air in the body will enable the body to float but this test is trying find out how much the body floats due to the body fat and not the air inside the body .
Hydrostatic Weighing produces fairly accurate results and thus can be used to chart progress .
Hydrostatic Weighing requires a lot of equipment as well as space . The test itself is time consuming and involved . Also , in-depth knowledge is required to administer the tests as well as to compute the calculations . Lastly , being submerged under water may prove to be difficult for some .
Hydrostatic weighing will cost anywhere from $10-$75 due to the involved nature of the test.
Places to go
Available at research institutions and colleges or universities
Discounted pricing is usually available for students.
Source : http://www2.gsu.edu/~wwwfit/bodycomp.html