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How Much To Ship Priority Mail Medium Flat Rate Box?

The good news about finding out how much it is to ship Priority Mail medium flat rate box to your destination address is that USPS has standardized the cost. For most US addresses the cost of the shipping for this box size is the same no matter where it goes. Prices will change for international and APO/FPO addresses.

Do I Have to Use an Official USPS Box?

Yes, you do have to use an official USPS box. You cannot use your own box even if it has the exact same measurements as the official one. The good news is that these boxes are provided for free by USPS. You can get your box right when you ship your package, or you can order the boxes in advance and have them delivered to you. USPS does this as their boxes are specifically designed to promote safe transport, and to allow for accurate logistic preparations. This is why only USPS issued boxes can access this rate and delivery service.

How Much to Ship Priority Mail Medium Flat Rate Box?

Medium Flat Rate Boxes cost $12.35 when you purchase the postage at a USPS retail outlet, or $11.30 if you get the postage online. There are two different size boxes that you can choose from:

  • 11″ x 8-1/2″ x 5-1/2″ Inside and 11-1/4″ x 8-3/4″ x 6″ Outside
  • 13-5/8″ x 11-7/8″ x 3-3/8″ Inside and 14″ x 12″ x 3-1/2″ Outside

That online cost can be improved if you have a commercial account or use an online discount postage provider. Both access discounts accorded for volume shipments.

What About the Cost for APO/FPO Shipments?

If you are shipping to a military or federal address there is only one choice in medium flat rate box size.

  • 12″ x 12″ x 5-1/2″ Inside and 12-1/4″ x 12-1/4″ x 6″ Outside

This box is also available through retail locations or online. The retail cost is $15.45 and the online purchase price is $13.80. Discounts on that price are available if you access volume discounts through a commercial shipping account with USPS, or by having an account with an online postage supplier like or Endicia. (Learn more about medium box flat rate shipping cost.)

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