Mail Services Web Site, U.S. Postal Service: Envelopes

APPROPRIATE SIZE AND STRENGTH

Enclosures will determine the appropriate envelope to be used, meaning the envelope will be one of the right size and strength.

The size should properly accommodate the insert(s). Excessively large envelopes will not keep the inserts firm. The inserts in such envelopes slide about, create an imbalance of the envelope, risking ripping and loss of contents. A snug fit keeps the enclosure firm in the envelope providing for effective mail handling.

Conversely, when an envelope is overstuffed it can burst at the seams when machine processed. The result can be a total loss of the mailing.

The strength of the envelope should be such to withstand the weight of its contents. If there is stress at the seams or sharp edges, the envelope is in an overload condition where it can burst or tear apart and lose its contents.

LETTER SIZE

Letter size envelopes must be rectangular in shape for automated processing by United States Postal Service.

The following dimensions must be met for automated processing by USPS:

Minimum Maximum

Height: 3 1/2 inches 6 1/8 inches

Length: 5 inches 11 1/2 inches

Thickness: .007 inch 1/4 inch

Nonstandard Size

Letter-size First Class Mail or single-piece -rate Standard Mail (A) weighing 1 ounce or less is nonstandard and subject to the applicable surcharge if is thickness exceeds .25 inches or if, based on the placement (orientation) of the address, its length exceeds 11.5 inches, its height exceeds 6.125 inches, or its length divided by its height - the aspect ratio - is less than 1.3 or more than 2.5.

Aspect Ratio
(not drawn to scale)

FLAT SIZE

Flats are envelopes larger than 11 1/ 2 inches long by 6 1/8 inches high, but not larger than 15 inches long by 12 inches high.

INTERNATIONAL LETTER SIZE ENVELOPES

Mail in letter size envelopes for delivery to foreign countries should be placed in "International" Envelopes. These envelopes have red and blue borders. These envelopes should not be used for addresses within the United States.

ENVELOPE TYPES

Green Bordered - Used only for First Class Mail.

Red and Blue Bordered - Used only for airmail to foreign countries.

Plain White or Manila - Can be used for all other classes of mail. These must be clearly marked to show the class of mail. i.e., First Class or Standard (A) mail.

Padded - These envelopes contain a cushioned lining to provide a degree of safety for mailing small and fragile merchandise.

Priority - Should be used for First Class mail weighing over 11 ounces and other mail under 11 ounces requiring expedited delivery. (These envelopes are red, white and blue and available from Mail Services free of charge).