Scrappy 101 asked me what my 4-patch size is. She says she is getting different sizes as she sews.
Here is what I do:
My 4-patch is 2 1/2" unfinished.
Since I did not cut the swapped squares there are always a few that are either too large or too small.
I have a measuring tape applied to the edge of my sewing cabinet. Mostly I can eyeball what a 1 1/2" square looks like. If the two patches are not the same size I lay them on the measuring tape.
Too big is easy to fix with the scissors. I trim it .
Too small is another matter. I line up the outside edge of the too small square with the correct size square. If the difference falls inside the 1/4" seam I simply sew it that way. If it does not I throw it away.