You have to know your bodyfat percentage and bodyweight. If you get some calipers you can figure this out, HOWEVER it is very easy for people to make mistakes in calculations, and unless you have an assistant you are pretty much reduced to a 3 point test.
If you calculate 15% bodyfat and you are 200 pounds, thats 30 pounds of "fat." That is an estimate of course as there is visceral fat, but that is how we basically calculate it. Since bone density hardly changes, it doesn't bother me to call the rest LBM, and that is what people do. 30 pounds of fat and 170 pounds LBM.
The electro impedance scales are bogus, calipers or bust.