a common computation is to add 7/8" to the finished size for HSTs. This allows for a narrow trimming of the finished square to make sure your square isn't threads too narrow.

What great setting! I could make it in red white and blue and then add a couple of borders to get it bigger for a Veteran donation quilt.

sewsewchickie, no you're right. My point was that that method would work because of the number needed.