The description for this:Model stitched on 32 Ct. Glacier Linen by Picture this Plus, using DMC, Weeks Dye Works and Classic Colorworks floss. Stitch count 50x45.
Given the stitch count the dimensions on the suggested fabric is about 3 1/4" x 3" (rounded up a little). This is only the design size though so I would add at least 3" per side so you have enough for finishing.