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Guidelines: Non-machinable First-Class Mail

Important! For the most up-to-date and complete domestic and international mailing information, see the USPS website, the USPS Postal Explorer website, or your USPS postal representative.

Following are some sample guidelines:

First-Class Mail under 1 ounce is considered nonmachinable if one or more of the following conditions is met:

For example, a square envelope has an aspect ratio of 1.0 and would require the surcharge if it weighs under 1 ounce.