What Are the Sizes of USPS Flat Rate Boxes?

The United States Postal Service handles 47 percent of the world's mail, processing and delivering 506.4 million pieces of mail each day. Many of these mail items were shipped in Priority Mail flat rate boxes. Since there is no need to measure or weigh any of these boxes unless they are over 70 pounds, you won't have to guess how much it costs to ship your packages. Customers who use flat rate boxes are given handy tracking numbers and $50 in free insurance protection. When you're ready to mail your next package, choose from 12 types of Priority Mail flat rate boxes in a variety of sizes.


What Are the Sizes of USPS Flat Rate Boxes?
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Flat Rate Envelope

Flat rate envelopes measure 12 1/2" x 9 1/2" and are perfect for sending important work documents, financial papers and letters that don't fit in a typical envelope. The cost is $6.55 for commercial customers and $6.70 when brought to the post office or scheduled for shipment via the post office's website.


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Gift Card Flat Rate Envelope

If you simply want to send a few gift cards to friends or family members to celebrate their special day, use a gift card flat rate envelope. It measures 10" x 7" and sells for $6.55 commercially, or $6.70 when purchased in-store or online with the USPS.

Window Flat Rate Envelope

Choose between a window flat rate envelope that measures either 10" x 6" or 12 1/2" x 9 1/2". These envelopes have a clear window so you can insert and mail pre-addressed envelopes. You'll pay $6.55 if you're a commercial customer and $6.70 if you visit any USPS office or use the company's online website.


Small Flat Rate Envelope

When mailing passports or other small documents, you'll need the small flat rate envelope. It measures 10" x 6" and costs $6.55 when mailing commercially. Taking the envelope to the post office or scheduling a mailing through the USPS website will result in a charge of $6.70.

Padded Flat Rate Envelope

Should the item you wish to mail require a little protection, a padded flat rate envelope is the way to go. It measures 12 1/2" x 9 1/2" and can be used to send everything from necklaces to books to wallets. In a commercial setting, the price to ship this envelope is $7.10, while retail and online locations charge $7.25.


Essential legal documents, such as real estate contracts, are best mailed in a 15" x 9 1/2" legal flat rate envelope. The commercial base price is $6.85, while the retail cost, both in-store and online, is $7.00.

Small Flat Rate Box

Upgrade from an envelope to a small flat rate box if you plan on mailing a child's outfit, small electronic device or a few DVDs. The box measures 8 11/16" x 5 7/16" x 1 3/4" on the outside and 8 5/8" x 5 3/8" x 1 5/8" on the inside. The price is $7.05 for commercial customers and $7.20 for retail use.


Medium Flat Rate Box-1

Send your college student some school supplies, or even a new pair of shoes in this top-loading medium flat rate box, which measures 11 1/4" x 8 3/4" x 6" on the outside and 11" x 8 1/2" x 5 1/2" on the inside. Commercial customers pay $12.85, and retail and online customers pay $13.65.

Medium Flat Rate Box-2

Use the side-loading medium flat rate box with outside measurements of 14" x 12" x 3 1/2" and inside measurements of 13 5/8" x 11 7/8" x 3 3/8" to mail office supplies and toys. The cost is just $12.85 commercially and $13.65 at any USPS retail location or online portal.


Large Flat Rate Box

With outside measurements of 12 1/4" x 12 1/4" x 6" and inside measurements of 12" x 12" x 5 1/2", the large flat rate box is perfect for gifting a laptop or sending Christmas presents to out-of-town family members. You'll pay just $17.65 when mailing commercially and $18.90 when visiting the post office or scheduling the mailing using the USPS website.

APO/FPO/DPO Flat Rate Box

Want to send a package to a military member? Pay $16.15 commercially or $17.40 online or in-store for a box that measures 12 1/4" x 12 1/4" x 6" on the outside and 12" x 12" x 5 1/2" on the inside.


Large Flat Rate Board Game Box

Encourage game nights by using the large flat rate board game box that measures 24 1/16" x 11 7/8" x 3 1/8" on the outside and 23 11/16" x 11 3/4" x 3" on the inside. This box has a commercial base fee of $17.65 and retail and online fee of $18.90.