I just cut 2.5 inch strips from yardage--much cheaper than jelly rolls, and I can get exactly the shade of background fabric I want. You will need 12" of 2.5 inch strips for each charm (assuming 5" charms). Multiply that by the number of charms and you will get the total number of inches of 2.5 inch strips you need. Then divide by about 40 for the number of strips to cut. Remember to round up. Cutting the 2.5 inch strips isn't so bad, I got into a sort of rhythm and just cut, cut, cut. Any extra strips I cut I used for the binding.