us postal service priority mail box sizes refers to the various box sizes available for use with the USPS Priority Mail service. When users search for “US Postal Service Priority Mail box sizes,” they are typically looking for information about the different box options provided by USPS for their Priority Mail shipping. USPS offers several sizes of flat-rate boxes, including small, medium, and large options, as well as padded envelopes for lightweight items. Priority Mail boxes are available for free through the USPS website, and customers can select the appropriate size based on the weight and dimensions of the item they wish to ship. The flat-rate nature of these boxes allows customers to pay one price regardless of the weight of the package, provided it fits within the box. This makes it a convenient option for businesses and individuals who need to send products quickly and affordably within the United States or internationally.