Originally Posted by big john

It doesn't matter if it's a 58 or whatever size it's called. If you want to measure stack and reach, measure from the floor to the center of the bottom bracket, then from the floor to the top of the headset. Subtract first number from second for stack.

Back the rear wheel up against a wall. Measure from the wall to the center of the bottom bracket, then from the wall to the center of the headset. Subtract first from second for reach.

Frame size in cm could be measured from the center of the bottom bracket to the top of the top tube, or the center of the top tube, or with a sloping top tube, to the "virtual" top tube. Then there are frames measured in small, medium, large, etc. Sizes are confusing.