Originally Posted by John E
This is the "center-to-top" dimension, which, along with BB height and/or top tube standover height, helps determine a rider's fit to a particular frame. (Top tube length is the other critical fit dimension.) Many people prefer to quote "center-to-center" frame size, since frame angles and frame geometry are all measured from the intersections of the centerlines of the frame tubes. When buying a bike, make sure you know which dimension is being quoted.
Center to top of extended seattube is the way Fuji and a few others do it. Others are c-top of toptube and others are c-c. There is no 'standard.'