Purchase change-cals between1 and 100 square inches, OR101 and 200 square inchesDecide how big the change-cal needs to be to cover the area you want replaced. Example: A 5" x 12" change-cal that says (555) 555-5555 would be 60 square inches, and priced at $5.05 each for 25 or $3.30 each for 50 or $2.20 each for 100.