If you start with 5" charms to make your HST's, you'll end up with 4" HST's. 6" charms will end up as 5" HST's. With 5" charms you would need 10 across and 15 down for a total of 150 HST's. With 6" charms; you need 8 across & 12 down for a total of 96 HST's.