I also want to add that everyone has their own personal preferences.
Some barrel racers should technically have a 15" seat; yet they ride in a 14" or a 14.5" because they like that close contact. Or vice versa: You might have a barrel racer who should be using a 14" seat, but you find them riding in a 15" seat because they like the extra room.
A good rule of thumb is that when you are sitting relaxed in the saddle, you should be able to fit two fingers between your thigh and the swell.
That's a good point to start with, but again, everyone like a different "feel" to their saddle so they could go up or down from that point.
Height and weight might also have nothing to do with it. Someone might be fit and light, but have really muscular thighs, therefore requiring a larger seat size. Or someone might carry all their weight around their belly, but have little legs, and therefore need a smaller seat size.
Again, you can make a generalized guess on height and weight, but there's always going to be differences in body type that can make a difference.
Best thing is to go to a tack shop and sit in a lot of different sized saddles and figure out the size that feels the best for you.