Weight restrictions for Priority Mail Express International Flat Rate Envelopes are 4 pounds. Weight restrictions for domestic Priority Mail Express Flat Rate Envelopes, and Priority Mail Flat Rate Envelopes and Boxes are 70 pounds. Tape may be applied to the flaps and seams to reinforce the container provided the design of the container is not enlarged by opening the sides and the container is not reconstructed in any way. When sealing a Flat Rate Box or Flat Rate Envelope, the container flaps must be able to close within the normal folds.

Note: Flat Rate prices are available when material is sent in a USPS -produced Flat Rate Envelope or Box. USPS Marketing Mail Eligibility Decision TreeĪvailable for Domestic and International PRIORITY MAIL EXPRESS Flat Rate Envelopeġ2-1/2' x 9-1/2' Legal Flat Rate Envelopeġ2-1/2' x 9-1/2' Gift Card Flat Rate EnvelopeĨ-11/16' x 5-7/16' x 1-3/4' – Outside Medium Flat Rate Boxesġ4' x 12' x 3-1/2' – Outside Large Flat Rate Boxġ2-1/4' x 12-1/4' x 6' – Outside Large Video Box (Flat Rate pricing for international only)ĩ-9/16' x 6-7/16' x 2-3/16' – Outside DVD Box (Flat Rate pricing for international only).Designing Letter and Reply Mail (PUB 25).

Usps flat rate padded envelope rules