There are many different tools that are available to measure your fat. Not all tools are accurate but they do give you an idea of your body fat compositions.
DEXA (Dual Energy X-ray Absorptiometry)
The most accurate way on measuring your body fat is to perform a DEXA (Dual Energy X-ray Absorptiometry) test. This test is expensive and cost approximately one hundred dollars. However, it is considered to be the gold standard for measuring bone density and bone fat (with a 2-3% margin of error).
Hydrostatic Weighing
Another slightly less expensive test is the hydrostatic weighing test. This test works by getting you to sit inside a tank of water and make you blow out air as much as you can. It has a accuracy rate of 97-98% and cost in the range of $25-$50. If you have severe breathing problems it is best to choose other methods because of the amount of breathing exercises you need to perform.
Bioelectrical Impedance
This is the most easiest and painless ways to determine your body fat content. It is measured by using an electronic device that shoots signals from foot to foot or hand to hand. If there is a lot of body fat then the signals will travel slower.
Body Mass Index (BMI)
The body mass index was invented between 1830 and 1850 by Adolphe Quetelet. It became a popular measurement of a person's fitness because it is simple to calculate and doesn't require expensive equipment. Ever since obesity became prevalent in 1950's and onwards, it widely used by the medical authorities and health insurance companies to compare groups of people.
The formula used to calculate an individual BMI is to measure body weight divided by the square of their height (using the metric system).