RC, this is so hard. I've been trying to get an accurate measure of my bf for months. What I'd suggest is to use the same type of measurement--e.g., body fat scale, bioelectrical impedance, manual measurement--and compare the results over time. Every single style of measurement, with the possible exception of immersion in water which is very expensive--has a large margin of error. So you can't get a really trustworthy absolute measure, only a comparative one over time.

BTW, body mass index and percentage BF are two completely different standards and you really can't make much out of one standard alone. An athlete who's very muscular could have a high BMI but a very low BF%.

Another way of "ballparking" the BF stuff is just to notice how differently your clothes are fitting over time, as you lose fat and gain muscle.

HTH!