The USPS is redefining letter-size booklets. New size and tabbing requirements took effect September 8, 2009. A booklet consists of multiple sheets or pages that are bound by a saddle-stitching, perfect binding, pressed glue or other binding method that creates a nearly uniformly thick mailpiece. The new requirements apply only to letter-size booklets, not larger booklets or unbound folded self-mailers. • The minimum height is 3.5 inches and the maximum is 6 inches. • The minimum length is 5 inches and the maximum is 10.5 inches. • The minimum thickness is .009 Inches and the maximum is .25 Inches. • 3 tabs required, minimum 1 ½ inch diameter, non perforated (currently 1" diameter and can be perforated).