The amount of wafer seals on a self-mailer depends on the size of the piece. For example, a typical self-mailer can measure either 5.5” x 8.5” or 6” x 9” in size. With a fold on the bottom and an open end on the top, two wafer seals are required. Mailers that are provided with saddle stitching require 3 wafer seals. Flat size mailers do not need any wafer seals per postal requirements.