What I've done, that works best for me, for a 16x19 is count 8 racquet lengths for the mains and 7 racquet lengths for the crosses. For an 18x20, I do 8.5 racquet lengths for the mains and 7.75 racquet lengths for the crosses. For a 1 piece, I do 6 wingspans (I'm about 6') and my forearm for a...