After you have removed the seams, worn spots, pockets, zippers, etc. lay out the denim like you would a regular fabric square it up and cut it into the size of squares you want. I made a simple 4-patch with 8" squares denim and upholstery fabric, the best size I could get out of legs of a size 40"x32" pair of jeans, which is now in my car for winter emergency and picnic.