It's amazing how many answers you have so far.
I agree with PaperPrincess - if you want HST's that finish at 4.5" to go with the 5" unfinished squares, add 7/8" to the finished block size of 4.5", giving 5 3/8". Many quilters will add an extra 1/8" (giving 5.5") and trim the HST slightly after sewing.