Mailing 101

Mail Piece Design

Letters, flats, and postcards must meet the following requirements:


USPS Postcard Size Chart

Length: 5 to 6 inches across

Height: 3½ inches to 4½ inches tall

Thickness: .007 to .016 inches thick


USPS Letter Size Chart

Length: 5 to 11½ inches across

Height: 3½ inches to 6⅛ inches tall

Thickness: .007 to .25 inches thick


USPS Flat Size Chart

Length: 11½ to 15 inches across

Height: 6⅛ inches to 12 inches tall

Thickness: .25 to .75 inches thick


Self-mailers can be cards, folded brochures, catalogs, or any other piece that is not enclosed in an envelope. We recommend a 'clear space' of 3 ½ inches high, and 4 inches wide on self-mailer pieces. This space is used to display the delivery address, postage, and return address. For folded self-mailers, the fold must be on the bottom or leading edge of the piece. For tri-folded self-mailers, the delivery address must be on the middle folded panel.

Bottom Fold

USPS Self-Mailer

Leading Edge Fold

USPS Self-Mailer

Postal Endorsements

Ancillary service endorsements are used to tell the Post Office what to do with a mail piece that is undeliverable is addressed. Deciding which endorsement to use (if any) can be confusing, and choosing the wrong one can be costly. For detailed information on postal endorsements, please visit the Endorsements page.

OCR Scan Area

Postal equipment scans all flat and letter pieces from the bottom of the piece upward. Because of this, it's important that the area below the delivery address be clear. If the piece is not already barcoded during the addressing process, the Post Office will apply their own barcode in the space to aid in routing the piece to it's destination.