The Priority Mail flat rate boxes carry the most variety in size: from small windowed envelopes to large envelopes for legal documents, and small, medium and large boxes in side-loading and top ...

11″ x 8-1/2″ x 5-1/2″ Inside11-1/4″ x 8-3/4″ x 6″ Outside 13-5/8″ x 11-7/8″ x 3-3/8″ Inside14″ x 12″ x 3-1/2″ Outside $19.30 $19.91 Large Flat Rate Box; 11-3/4” x 12″ x ...

The new Priority Mail Large Flat-Rate Box (12" x 12" x 5 inches or 800 cubic inches) will be available in Post Offices nationwide beginning March 3, but customers can begin ordering them Feb. 20 ...