I just found a terrific website:
I was trying to figure out dimensions to cut squares to finish as a 3-inch square on point in a square block for a quilt I’m working on. I put in the desired finished size (3) and it calculated sizes for the central square and outer squares to cut diagonally. I imagine it calculates sizes and yardages for other blocks, too. Yes, a flea who finished ninth grade could calculate this, but I’m just getting by on my looks so forgetaboutit.