One of the most common questions asked of those who are into fitness is "What is your body fat percentage?" Body fat percentage can be measured in several ways. There is DEXA (dual energy X-ray absorptiometry) huh? Hydrostatic weighing, calipers (aka pinch test), bioelectrical Impedance, and of course those fancy handheld contraptions that you enter your height, weight and age, grip the handles, and it spits out a number. The latter is about as accurate as the sex-appeal meter at the arcade. The others aren't a whole lot better.
The problem with body fat testing is that the two most accurate ones, DEXA (scans your whole body and bone density) and hydrostatic weighing (where your entire body is submerged in water on a scale and you exhale as much as possible), both have a margin of error of 2-3%.....So assuming you are 8% body fat, your results can be off by as much as 37.5%! To put that in context, that's like weighing yourself on a scale when you weigh 200 lbs, and the scale tells you that you weigh 275 lbs keep in mind; this is the most accurate form of testing.
The most common and cheapest form of testing is the calipers, or skin pinch test. Assuming you have the world's leading expert on body fat testing with calipers, the best you can hope for is a margin of error of 4%. Realistically, you can make the results whatever you want them to be, so if it reads too high for your ego, just pinch less skin and POW, you just got leaner. This explains why there are so many people walking around the gym claiming 3-4% body fat.
Ultimately, body fat testing can be a useful tool to measure changes in your own body fat. This is assuming that you perform each test as similarly as you can to the one previous. This way, you can get a fairly decent idea of your progress and changes in your body fat percentage. To find out your actual body fat at any given point, however, measurements can give you a vague idea and that’s about it. Then again, so can a mirror.