Body Fat Percentage Calculators

The problem with tracking your body fat percentage to an exact number is that most methods of body fat measurement just aren't that accurate. When you measure the circumference of certain areas of your body, you're attempting to compare yourself to a model typically based on weight and the measurements you've mentioned. The problem with this is that there is no way to know how much of any weight you have is attributed by fat, muscle or bone and even water. There are more accurate ways of measuring body fat, for example, calipers which pinch the skin and narrow the window used to compare yourself against a model, but they're prone to user error and are still not terribly accurate (although they tend to me much more accurate than the weight/circumference method). There is also something called hydrostatic tanks that measure your body fat, but they're expensive and unless your local gym has one you can use and you're trying to do something very technical or in a demanding competition it's, in my opinion, not worth the effort.

The most important thing to take from body fat measurements is the ability to see a trend. Measure yourself very often, like once in the morning and once at night (this works great with calipers) and be sure to be consistent with not only the method you use (circu., calipers, hydrostatic), but also be consistent with the exact way in which you measure yourself. After a while of doing this, even if numbers vary a bit, it will be clear when a trend emerges and you should be able to identify what's allowing/helping the trend continue.

TL;DR -- In short, the numbers don't matter aside from health concerns; work on identifying trends.