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

Under 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. At least one of the following extra services must be combined with Hold For Pickup service: USPS Tracking, Signature Confirmation, Adult Signature Required, Adult Signature Restricted Delivery, or Insurance.

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.