Here is a really good site if you would like to know your body fat % and how to take the measurements.
You'll need body fat calipers in order to take your measurements but it's really easy to do. This one here runs $29.95 on this website and comes with a measuring tape to which is really nice I bought a kit like this and love it. Amazon has it for $25.00:
My husband and I did our body fat measurements last night and it took maybe 10 min. We did three measurements in each of the seven places and took the average of each measurement. We both ended up having around 16% body fat, that put him at a fitness level and me at athlete level.
Body fat % is good to keep an eye on when you are losing weight because you will be gaining muscle which weighs more then fat. It may appear some weeks that you are not losing when really you are losing fat and gaining muscle. It is not necessary to do though my dad lost the weight he wanted to without this tool but would ask me why he was not losing some weeks. I would always reply if you want to know what is really going on with your body then do your body fat % and that will tell you.
There are some times when your body just won't let go of the fat so you just have to keep at it and know that you will see the results you want if you are patient. It's hard I know but it is worth it! If you find you are not losing you may need to do one of three things, clean up your diet, hit the workout harder, or try mixing up your workout. Instead of hitting the treadmill like you always do jump rope or do the bike. Mix it up keep your body guessing lol.