The easiest way to measure body fat is either calipers or a hand held device. Both have a margin of error of about 3%.
The handheld device can have a larger margin of error depending on your hydration level, sodium level, food intake, temperature, etc.
Caliper measurements need to be taken in at LEAST 3 areas and then averaged out. A professional should do this for you as most people pinch muscle and fat or not enough skin.
Both can be found at Amazon.com and both are cheap. Both give estimates, but for most people... that's all that is needed. The number is not as important as the "level" you are in. Healthy, obese, normal, etc.
The most important thing is the pattern. So long as the body fat continues to decline (to safe levels). Do a search at Amazon for "bio impedence" or "hand held body fat analyzer". I like Omron's for around $30.