Okay. I got 13" to the center of the chrome piece and 14" to the bottom! I am NOT taking that thing apart to measure the actual size from top to bottom!!
I think it's fair to say you have a 14" windshield on yours. I'm going to a 14" since the 12" is too short. I get a windblast at highway speeds that hits me in the forehead and I can see way over the top of if, so I'm hoping the 14" Clearview with recurve will end up being perfect for me.
You didn't say for sure what brand you're looking at, so one thing to keep in mind if you are looking at one of the other shields mentioned in this thread, if the shape/angle of the shield is different from stock, that is going to throw a whole different variable into play as far as what height would be best.