The size of the finished piece will depend on the yarn used and type of filet stitch grid you make.
A No.10 thread and a 1 X 1 filet grid (1 post stitch & 1 block or space) will produce a much smaller square than using a worsted weight yarn and a 1 X 2 filet grid (1 post stitch & 2 blocks or spaces)
I have included the basic instructions for making a 1 X 1 filet grid and a 1 X 2 filet grid. The sizing information is for a 1 X 2 filet grid.
Use the hook required for the size of yarn/ thread chosen
Remember you could also use the graphs for tapestry crochet, beaded crochet, tunisian filet crochet, embroidery even knitting!