I've read two posts about how to measure seat height. Both claiming to "simplify" the process. The two are more of less the same: stand up against the wall, stick a dowel between your legs, cram it up against your sit bones, measure the distance between the dowel and the floor, multiply by something, subtract something else, and then measure that sum from the ground to the seat. Simply as, I don't know, something hopelessly complicated.
Here's the simple version and it works: Put on your cycling clothes and shoes, sit on the seat, put your heel on the pedal, lock your leg straight with pedal at its lowest point, adjust the seat so your butt rests solidly on it. Now ride with the ball of your foot on the pedal, and you should have power during the whole circle. If not lower or raise the seat just a bit until you do.
Works like a charm.