The calculation for making HST is that you add 7/8" to the FINISHED size. So to make 4" finished HST, you would add the 7/8, which gives you 4 7/8. Since most folks don't really want to cut odd size squares, they round up the 7/8 to one inch, sew and then trim and square them down a bit to 4.5" (which finish at 4"). Since you trim all sides of the finished patch, you are only trimming off 1/16". Just a sliver.
So basically, if you want to make 4" finished HST, you cut 5" squares.
Last edited by PaperPrincess; 02-28-2014 at 03:14 PM.