Non-Machinable Stamps

Non-machinable stamps are intended to help pay the postage for First-Class Mail letters that trigger the USPS nonmachinable surcharge. Common reasons include square shape, excessive rigidity, an uneven surface, or other characteristics that prevent normal machine processing.

Identify the mailpiece first

A stamp labeled for a nonmachinable surcharge does not automatically make every unusual envelope acceptable as a letter. The piece must still fit the applicable letter standards. If it is too thick, too rigid, or otherwise outside those standards, it may be priced as another mail class.

Typical situations to check

• Square greeting cards or invitations.
• Clasps, buttons, pens, keys, or uneven contents.
• Rigid inserts that keep the envelope from bending normally.
• Address orientation or shape outside standard processing rules.

Rates can change, so compare the stamp's current postage value with the required surcharge and base letter postage. When uncertain, take the finished piece to a Post Office or use the USPS calculator.

Page reviewed: August 25, 2026. Product availability and postal rates can change.