If you're going to measure your inseam for cycling, the right way to do it is to get up against a wall, push a hardcover book against the wall, and then slide it up into your crotch, pushing hard enough for it to be somewhat uncomfortable. (Not kidding). Then, measure the height of the book from the floor. The fit formulas all assume a measurement of this type.

Another method to find the right ball park is, get seat height so your heels can barely touch the pedals at the bottom of the downstroke.

Really though, the only way to get fit perfect is to experiment. Once you have your saddle in the right ballpark, moving it up or down 1/8" can make a huge difference (good or bad) so remember to keep adjustments small.