Body Fat Percentage
Body Fat Percentage is calculated from the two compartment model’s equation of the body, which shows that the body is built up of two components: one is the fat mass (the total fat of an individual) and the other one is the fat-free or lean body mass (everything else: bone, water, lean tissue, etc). The first and maybe the best method is Hydrodensitometry or underwater weighing. First the dry weight of a person is measured in minimal cloth, then the person is lowered on a chair into a tank full of water (of course with a nose clip), and their weight is measured again, in the water. In fact in this way we can measure someone’s body density with the following formula:

As it is difficult to measure one’s body density in this way, as such tanks can only be found in research centres, there are some other methods which can be applied such as Dual-Energy X-Ray Absorptiometry (DEXA), Total Body Potassium (TBK), Magnetic Resonance Imaging (MRI), Total Body Electrical Conductivity (TOBEC), Computed Tomography (CT), but all of them need special equipment or, at least drawing of blood. In recent years a new method has been found for obtaining a good assessment of body composition, this is Bioelectric Impedance measurement. This device has many types for research goals, but some of them are made for home-usage. They use software for the measurement and evaluation.
How can you get a closer evaluation of your body composition in an easier way at home?
There are two methods which can help you, the first is the Girth measurement for which you will only need a tape measure, and the other one is the Skinfold measurement, for which you will need a special, but not expensive device called a skinfold caliper. Although the latter one needs more preparation, its results are closer to the truth.

Girth Measurement            Skinfold measurement (Pinch test)