Im a sophomore in hs and do LJ and jumped 17'10" from the back of the board? so...?

i had like 3 inches of my foot at most on the back of the board, it was one of those wider boards like 1 2/3 feet or somethin and got almost 18, would i have jumped like high 18 or low 19 if i was up on the board all the way? im guessing yes and also how wide exactly are the bigger boards?