So, without seam allowenses the block will be 5 inch.
However you do your math, it will be a strange size for the patches. 5 inch devided by 3 equals 1.66666 .inch. Then you have to add 2x seam allowense. Or you could say 1 block is 1 2/3 inch excl. seam allowens.
As I said, very strange size.
But I could be completely wrong of course :-)), after all, I'm only dutch ROFL (yep, that's my excuse)