Priority Mail Large Flat Rate Boxes
Inside Dimensions Outside Dimensions
12" x 12" x 5-1/2" 12-1/4" x 12-1/4" x 6"
23-11/16" x 11-3/4" x 3" * 24-1/16" x 11-7/8" x 3-1/8" *

*Packaging is only available online at


Priority Mail offers 1 day, 2 day, or 3 day service to most domestic destinations. Select Priority Mail Flat Rate Boxes are available at many Post Offices. All packaging can be ordered online at This 1-3 day service may include tracking at no additional cost. Priority Mail bearing an IMpb or retail tracking barcode includes $50 of insurance. Priority Mail bearing an IMpb paid at Commercial Plus prices includes $100 of insurance. Additional merchandise insurance up to $5,000 may be purchased for a fee.

Domestic Prices

Priority Mail Flat Rate Boxes are priced low to U.S. destinations, regardless of the actual weight of the piece up to 70 pounds. Customers must use USPS-produced Priority Mail Flat Rate Boxes to qualify for Flat Rate pricing.

Online shipping convenience
Hold For Pickup Service

Hold For Pickup service, Priority Mail items are held at a destination Post Office location for pick up by a specified addressee or designee. Upon arrival of the mailpiece at the destination Post Office pickup location, the addressee will receive an email notification from the Postal Service.

When sealing a Priority Mail Flat Rate Box, the container flaps must be able to close within the normal folds. 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.

APO/FPO/DPO Priority Mail Large Flat Rate Boxes

The APO/FPO/DPO box can be identified by the two markings, "APO/FPO/DPO Flat Rate Box" and "" Price discounts are available for this box when sent to APO/FPO/DPO destination addresses.