Practical Ecommerce

Shipping Rates: Flat Rate Boxes Usually Save Money

U.S. Postal Service flat rate envelopes and boxes can be a big money saver under the right circumstances. But you have to be careful. That’s because there are now seven domestic USPS flat rate size and rate combinations, and potential cost savings depend on a fairly complicated comparison of package volume, weight and distance.

Use a Spreadsheet to Compare Rates

The easiest way to manage this problem is to create a spreadsheet that presents all the rates in one document. There is a flat rate mail comparison chart that I use and you are welcome to download a copy by clicking here.

Screen shot of flat-rate spreadsheet.

Screen shot of flat-rate spreadsheet.

How to Shop Flat-rate Shipping

  • Step 1 – Pick a flat rate envelope or box that will contain your shipment, loosely. Pack the items and then weigh the package and contents.
  • Step 2 – Find the priority mail charge by weight and zone on the spreadsheet, and compare this to the flat rate for the smallest envelope or box that works for your shipment.

For example, if a medium flat rate box (FRB1) that is 11″ x 8.5″ x 5.5″ is large enough for your shipment, and if the ship weight is 5 pounds with a zone 3 delivery address, you can quickly compare the $8.15 priority mail rate to the $10.35 flat rate. In this case, you would waste money by shipping at the flat rate.

But, if the delivery zone for that 5-pound package was instead zone 8, the priority mail rate increases to $17.50. So, using a flat rate box in this case would cost much less.

You can also add UPS or FedEx ground rates or USPS first class mail, media rate and parcel post rates if you anticipate using these other delivery options in place of USPS priority mail delivery.


The extensive range of U.S. Postal Service flat rate envelopes and boxes can be a huge money saver if you ship in volume, but it also pays to shop flat rate shipping against regular delivery costs on a shipment-by-shipment basis.

John Lindberg

John Lindberg

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  1. Michael J. Kaye September 1, 2009 Reply

    I’ve found the post office to be the cheapest for anything under 2 pounds. Especially if you can fit into the $4.95 flat rate envelope or box.

  2. Susan Eastin September 3, 2009 Reply

    The flat-rate envelope and small, flat-rate box for $4.95 are perfect for shipping 1-3 of our products. The cost is low enough for us to secure small orders. However, when we need to make the leap to a medium, flat-rate box, the cost more than doubles to $10.35. (We do receive a small discount when we purchase postage at When the cost is at this level, I’ve found that our FedEx rates are usually the same or less for a package averaging 15 lbs, depending on the package’s destination. With FedEx you also receive much better tracking capabilities and declared value coverage up to $100 at no additional charge. Right now we offer our customers the option of U.S. Priority Mail on smaller orders that weigh 11 lbs or less. Because our customers can compare rates and select between FedEx and USPS during checkout, not very many of them select U.S. Priority Mail if they’re at or above the $10.35 mark. FedEx Ground is often cheaper.

  3. tekgems December 7, 2010 Reply

    USPS is coming out with a Flat Rate Envelope LEGAL in 2011. This will allow you to have even more FRE stuffing opportunities. Many manufacturers forget to consider shipping dimensions in the design process. If they did, they have a competitive advantage over other manufacturers. In the end, with all things being equal, I will create packaging that can fit strategically inside a Flat Rate envelope when the product can’t be shipped via by less expensive methods. Even if your product is smaller than a Flat Rate envelope, think about your packaging so perhaps multiple quantities could fit in a Flat Rate envelope. Flat Rate is one of the best inventions of the post office — more manufacturers should take advantage of the shipping method.

  4. Brian March 10, 2016 Reply

    Is there an updated spreadsheet with shipping rates?

    • Kerry Murdock February 14, 2017 Reply

      We’ve just corrected the link to John’s spreadsheet, Brian.

  5. Shirlie Elliott June 21, 2017 Reply

    What is the current rate for the medium flat rate “if it fits, it ships” box?