Thanks AvaJoy - Their website recommends:

14" x 14" for cats and small animals
24" x 24" for cats and small to medium dogs
36" x 36" for medium to large dogs

These sizes are just guidelines. The actual Snuggles don't have to be exact. They could be made out of acrylic yarn or cotton in any pattern or color that you choose. The ends should be double-knotted and fastened off long and woven through the work to prevent unraveling from washing and wear. They are best when they are made thick for comfort and warmth.