it's in the eye of the beholder.....whichever looks best to you and gives good balance. It is difficult to visualize without seeing a picture and know what sizes would balance the block designs. Also the amount of fabric you need depends on whether you cut he length of the fabric to avoid seams or cross and will put seams in the batting. Initial reaction is if you do a 6" border cutting cross of the fabric you will need a minimum of 46" plus some. But don't take my calculations. You need to measure the exact and do the calculations from that.