Read Also: USPS Priority Mail Regional Box Explained What Boxes Can You Use Sending USPS Priority Mail? Regional Rate boxes have a weight limit of 15 pounds for Regional A and 20 pounds for Regional B. There are two types of Regional Rate boxes, A and B, to determine the price. USPS Regional Rates use zoning for distances. You can ship up to 70 pounds, regardless of distance as long as the item fits inside the box or envelope. USPS Priority Flat rate has a set price with each predetermined box size and type of envelope. Priority Mail Cubic uses the cubic volume of your package and the distance it is traveling to determine the price. Regular Priority Mail uses the weight and dimensions of your package and the distance that the package is traveling to determine the shipping price. This includes regular Priority Mail, Priority Mail Cubic, Priority Flat Rate, and Priority Regional mail.

USPS Priority mail is a service with a shipping time of 1 to 3 days. The simplest way to understand the difference between USPS Priority Mail vs Priority Flat Rate is to think of USPS Priority Mail as the umbrella service for all Priority Mail.

Usps flat rate shipping time