Originally Posted by bearisgray

Try a sample using 4-1/2 inch squares - you might need to trim up the finished block a bit - but not by much.

The reasoning behind that number:

7-1/4 inch block = 29/4

29/4 / 2 = 29/8 -> which is half the width of the block

29/8 + 1/4 (for the seam allowance on one side) + 3/8 (for the triangle point) =

29/8 + 2/8 + 3/8 = 34/8 = 4-2/8 = 4-1/4

Technically, a 4-1/4 inch square should work. I prefer to cut a bit larger and cut down the HST to size.

Your assembled HST squares should measure 3-7/8 inches before sewing them into the pinwheel units. (Assuming "perfect" 1/4 inch seams and other measurements)

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Will the "finished size" of your 7-1/4 inch squares be 6-3/4 inches?

Or another way of figuring it:

IF the finished size of the 7-1/4 inch squares will be 6-3/4 inches:

1/2 of 6-3/4 =

1/2 x 27/4 = 27/8 = 3-3/8 -> the finished size of the HST square unit

27/8 + 7/8 = 34/8 = 4-2/8 = 4-1/4 -> the theoretical size to cut the squares