Details About USPS Flat Rate Boxes

by Jennifer Spirko; Updated September 26, 2017
The U.S. Postal Service offers a variety of flat-rate mailers for Priority Mail shipping.

The U.S. Postal Service promotes its flat-rate shipping boxes in a series of commercials as a convenient option, telling consumers, "If it fits, it ships." In contrast to traditional shipping methods, flat-rate boxes are priced by size, rather than by a formula derived from the weight, size and distance. Customers can order Priority Mail boxes, free of charge, or pick them up at any post office; they arrive folded flat but are easy to pop out and assemble. To qualify for flat-rate shipping, items must weigh less than 70 pounds and fit entirely inside the official U.S. Postal Service-provided boxes.

Small Box

The smallest Priority Mail flat-rate box measures 8 5/8 inches long by 5 3/8 inches wide by 1 5/8 inch deep. As of January 2011, this box costs $5.20 to mail anywhere in the U.S. The USPS suggests that this size is useful for small items like jewelry, brochures and small electronics, such as phones, music players and hand-held game systems.

Medium Boxes

The medium USPS flat-rate boxes come in two shapes. The deeper medium box measures 11 inches long by 8 1/2 inches wide by 5 1/2 deep, while the thinner one measures 13 5/8 inches long by 11 7/8 inches wide by 3 3/8 inches deep. Either of the medium boxes costs $10.95. The roomier sizes and two shape options give you many more options for shipping; the postal service recommends these for clothing, audio-visual equipment, computer components, shoes or office supplies.

Large Boxes

The largest Priority Mail flat-rate box comes in only one shape, measuring one foot long by one foot wide by 5 1/2 inches deep. It costs $14.95 to ship anywhere in the U.S., but there is a discount for mailing to military addresses designated APO, FPO or DPO; shipping to those destinations costs only $12.95. Thanks to the discount, the postal service suggests this largest box for sending "military care packages"; other recommendations include laptop computers and small ovens.

Regional Flat Rate

A newer flat-rate Priority Mail option is "Regional Flat Rate." According to a March 11, 2011, press release by the USPS, Regional Flat Rate "combines the speed and convenience with pricing depending on the delivery destination zip code." Option A boxes can weigh up to 15 pounds, while Option B boxes can weigh up to 20 pounds. There are two shapes of A boxes: 13 1/16 inches long by 11 1/16 wide by 2 1/2 inches deep or 10 1/8 long by 7 1/8 inches wide by 5 inches deep. B boxes also have two shapes: 16 1/4 inches long by 14 1/2 inches wide by 3 inches deep or 12 1/4 inches long by 10 1/2 wide by 5 1/2 inches deep. The specific rates will depend on your location and the package's destination.

About the Author

Jennifer Spirko has been writing professionally for more than 20 years, starting at "The Knoxville Journal." She has written for "MetroPulse," "Maryville-Alcoa Daily Times" and "Some" monthly. She has taught writing at North Carolina State University and the University of Tennessee. Spirko holds a Master of Arts from the Shakespeare Institute, Stratford-on-Avon, England.

Photo Credits

  • Siri Stafford/Lifesize/Getty Images