Mound Vs Flat- MPH

Does anyone know approxiamtely how many MPh’s are gained from flat ground to Mound. My 15 yr old hit 78 cold from a Stand still. I thought maybe two or three. Any thoughts?

Try this. Get a good catcher, have him set up behind the plate, and get a good pitching coach-perhaps a major leaguer—with a reliable stopwatch, to track the experiment. Have the kid throw from flat ground for about ten minutes, using all the stuff he has, and then from the mound for another ten minutes (with a quick break in between). Then check with your pitching coach for comparisons and see what you’ve got. 8)