Postage
Your invitations or cards should be weighed for postage before mailing. When items are added to the envelopes, the weight can increase. Also, special shaped invitations, such as square and oversized, require additional postage.
The minimum size for First-Class Mail is 5 inches long, 3-1/2 inches high, and 0.007 inch thick.
The maximum size for First-Class Mail is no more than 15 inches long, or more than 12 inches high, or more than 3/4-inch thick.
Square envelopes of any size will require additional postage.
For more information regarding postage rates and fees, please visit
www.usps.com or contact your local post office.