USPS Priority Mail Medium Flat Rate Box is $16.65
USPS Priority Mail vs USPS Priority Mail Large Flat Rate Box
Is it cheaper to ship using your own box or use the priority flat rate boxes?
USPS rates are skyrocketing, soon.
What are USPS Flat Rate Boxes and how does the pricing work?
USPS Flat Rate Boxes charge a single fixed price regardless of weight (up to 70 lbs) or destination zone within the United States. The price depends solely on the packaging type you choose. A 2-pound package from New York to New Jersey costs the same as a 50-pound package from Miami to Alaska using the same box type. Commercial pricing (available through Shopify Shipping or platforms like Pirate Ship) saves 10-26% versus retail rates. You must use official USPS-produced Flat Rate packaging and cannot substitute your own boxes of equivalent dimensions.
What are the available Flat Rate box sizes and their prices?
As of 2026, USPS offers several Flat Rate options: Flat Rate Envelope ($10.30 commercial), Small Flat Rate Box at 8-11/16" × 5-7/16" × 1-3/4" ($11.20 commercial), Medium Flat Rate Box in two configurations at 11.25" × 8.75" × 6" or 14-1/8" × 12" × 3-1/2" ($19.60 commercial), and Large Flat Rate Box at 12.25" × 12" × 6" ($28.70 commercial). All support up to 70 lbs maximum weight. USPS provides these boxes free through usps.com or local Post Office locations.
When do Flat Rate boxes actually save money versus standard Priority Mail?
Flat Rate boxes save money when shipping heavy items to distant zones. Small Flat Rate ($11.20) beats standard Priority Mail for packages over 2 lbs to all zones. Medium Flat Rate ($19.60) wins for packages over 11 lbs to all zones, or 5-6 lbs to Zones 5-9. Large Flat Rate ($28.70) wins for packages over 18 lbs to all zones. The sweet spot is high-density products (tools, books, auto parts) weighing 5-20+ lbs traveling to Zones 5-9 where weight-based rates would cost $25-63.
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New USPS rates went into effect on 19 January, the commercial rate (what you can get using PirateShip, etc...) for USPS Priority Mail Medium Flat Rate Box is $16.65.
At least for the USPS Priority Mail Medium Flat Rate Box this does not look like a rate increase from last year.
So I am trying to sell an item that is about 5 pounds and it fits inside of the USPS Priority Mail Large Flat Rate Box. When selling this on ebay, under the shipping service, do I select USPS Priority Mail or do I select USPS Priority Mail Large Flat Rate Box? Under the estimated cost for USPS Priority Mail, it says $9.85 - $23.15, while the estimated cost for USPS Priority Mail Large Flat Rate Box is $17.40 - $18.90. I am assuming that, on average, the USPS Priority Mail option will be cheaper. Is this correct? Or am I required to use the USPS Priority Mail Large Flat Rate Box option if I am using that box that I got for free from USPS? Thanks.