I had to enlarge a full size to a queen size, and my quilt was in 16 inch blocks (Each block was quilted in itself). I just laid the top on the bed and figured out how many more rows of blocks I would need and went from there.
I also bought a yard to 2 yards extra of each color to make sure. If I have any left, I will make pillows, dresser scarf, etc., Good luck!