Letters that exceed the First-Class standard envelope maximum length, height, or thickness are charged large envelope (flat) prices. They are charged a nonmachinable surcharge even if they weigh less than 1 oz. Unusually shaped mail, like square or vertical envelopes, lumpy envelopes, rigid envelopes, and mail with clasps, string, or buttons, must be hand-canceled. Additional size restrictions apply depending on the type of mailpiece you're sending.Īdditional Charges for Irregular Mailpieces & Envelopes Nonmachinable Envelopes All postcards and envelopes (or flats) must be rectangular, otherwise an additional charge may apply.Maximum weight for First-Class Mail letters is 3.5 oz for large First-Class Mail envelopes, the maximum weight is 13 oz.Large envelopes (flats) start at $1.35.Oversized postcards need letter stamps, which start at $0.66.Standard-sized, rectangular postcard stamps start at $0.51.Square, oversized, or unusually shaped envelope stamps start at $1.06.Standard-sized, rectangular envelope stamps start at $0.66.

Standard Letter & Postcard Sizes See Insurance & Extra Services Letters One price for up to 3.5 ounces with commercially priced letters and cards.Eligible for Delivery Confirmation ™ services such as Certified Mail ®.

Usps large flat rate box dimensions