What Is the Difference Between USPS Parcel Post and a Flat-Rate Box for Shipping?

The U.S. Postal Service only sells flat-rate boxes for the purpose of sending Priority Mail. The Postal Service designates all other packages Parcel Post, now renamed Standard Post. It charges set prices for Priority Mail packages, while pricing for Standard Post packages is based on weight and distance.

Priority Mail packages typically arrive within three business days, states the Postal Service. In comparison, the estimated shipping times for Standard Post is two to eight days.

Generally speaking, shipping costs are higher for Priority Mail. However, Priority Mail includes labels and boxes that the Postal Service provides at no additional cost. All Priority Mail packages weighing 70 pounds or less cost the same flat rates. As of 2015, those rates are $5.95 for shipping a small box, $12.65 for a medium-sized box and $17.90 for a large box.

Packages sent by either Priority Mail or Standard Post come with free tracking and optional signature tracking for proof of mailing and delivery. The Postal Service also offers Registered Mail, Certified Mail and insurance on packages sent Priority Mail for an additional fee, while only insurance is available for packages sent Standard Post. Customers also provide their own boxes and shipping labels when shipping packages using Standard Post.