You need to be tested by a qualified health professional.
There are 3 types of testing.
1. Electrical impedance. Most common testing method used today- you can even by BF monitors in pharmacists. Trouble is with these that they are uniformly rubbish and inacurate.
Pro equipment is more accurate, but even then ther are strict guidlines that must be met in order to get an accurate reading.
2. 4 point caliper test. When administered properly with good equipment it is very accurate. Takes a very skilled and practiced tester to get the best readings though.
3. Hydrostatic test. most accurate. Involves complete immersion in water. Can only be administered medically, the equipment is very expensive and very uncommon.
4. Best way of all. look in a mirror. We all know if have a little extra around the middle, you dont need it in black and white