The pattern calls for stitching on 30 count fabric over 2 Using this size the finished work would be 8 x 6 inches. Add three inches to each side (six horizontal and six vertical). You will need a piece of fabric that is 14 x 13 inches.

If you go with 28 ct over two stitches or 14 ct over one the finished area is 8.5 x 6.5 inches. You will need a piece of fabric 15 x 13 inches.

I have rounded the numbers up. There is not a lot of difference between the two sizes