Note: Actual inseam is not the same as your pant inseam.
The seat tube height is most important as it relates to your head tube. If your seat tube is too short, your head tube will almost certainly be too short. This results in too low of a handlebar position placing an inordinate amount of stress on your neck and back.
Note: Manufacturers measure seat tube in either center-to-center or center-to-top measurements. Which measurements is indicated inside each bikes sizing chart.