Do you have a grid type picture of the design? If so, count the # of squares across. Then multiply that number by the various possibilities of finished size squares, ie. if you use 4" squares it will be a finished size of 4x??, if you use 5" squares it will be 5x??, if you use 4-1/2" squares it will be 4.5x?? If your answer is a few inches short of the desired finished size then you can always add borders. On the one I Made for my DD I added a single border on the sides and triple borders on the ends.