2021 Rates

Details for 2021 rates for ShipStation users. Includes First Class, Priority Flat Rate, Regional Rate, and Priority Mail services.

USPS rates increased on January 28th, 2021. All USPS postage providers, including, must comply with these new rates. Listed below are some of the more common services that will see rate increases.

Below you'll find the 2021 rate tables for:

  • First Class Mail Packages

  • Priority Flat Rate

  • Priority Regional Rate Boxes

  • Priority Mail

Any size restrictions will also be listed in each section.

Check Weight and Dimensions

To avoid rate adjustments, ensure that you are using appropriate dimensions and weight for the service. Services classes can change weight and dimension requirements at any time.

ShipStation strives to keep up to date with carrier changes, but ultimately is not responsible for changes made to service limitations.

Visit USPS Mail Classes Comparison for the most updated information.

First Class Mail Package

If your package weighs less than 16oz and does not exceed 22" length x 18" width x 15" height (USPS measurement guide), it qualifies for First Class Mail.

First Class Mail rate are based on both weight and zone.

Priority Flat Rate

Priority Mail Flat Rate is a 1-3 day shipping service that charges one flat rate for your package/envelope, with a maximum allowable weight of 70 lbs. 

Priority Regional Rate Boxes

Priority Regional Rate Boxes have a zone-dependent flat rate. Depending on the zone you are shipping to, you may find the Regional Rate Box is cheaper. Essentially, Flat Rate Boxes are ideal for shipping long distances and Regional Rate Boxes are ideal for shorter distances.

Below are the costs of sending Regional Rate Boxes to each of the USPS's 9 zones. 

Regional Rate Box A: 10" x 7" x 4.75"

Regional Rate Box B: 12" x 10.25" x 5"

To view zones relative to your ship from location, use the USPS Domestic Zone Chart tool

Priority Mail Packages/Thick Envelope

Priority Mail package or thick envelopes are a great way to quickly, yet efficiently, ship packages that are under 70 lbs and do not exceed 108" in combined Length and girth (girth = the distance around its thickest part).

For information on cubic pricing for packages under 20 lbs and 0.5 cubic feet, please contact your account representative directly.

Notes on DIM and International Shipments

Keep the following in mind when using USPS services through

  • DIM Weight: When calculating dimensional weight, the weight divisor has been lowered to 166. The new formula to determine dimensional weight is (Length x Width x Height) / 166.

    • If DIM weight applies to your package, the carrier will compare the DIM weight and actual weight and charge the higher of the two for the label. For this reason, ShipStation recommends that you always enter the correct package dimensions when you configure your shipments. Thus, the rate you see in ShipStation will reflect the correct weight.

      If the label you print for your shipment reflects the incorrect rate as determined by USPS, you may be subject to the USPS Automated Package Verification. This can automatically deduct the difference in postage from your USPS postage provider account.

  • The Large Package type will represent any package type over the default dimensional weight threshold of one cubic foot.

    Dimensions are required if you use the Large Package type with the Priority Mail, Priority Mail Express, or Parcel Select Ground shipping services.

  • The Package package type will represent any packages that are one cubic foot or less, and will not require dimensions in ShipStation.

  • The maximum weight for a USPS First Class International shipment that uses the Large Envelope or Flats package type with Documents as the contents type is 15.994 oz.

  • The maximum weight for a USPS First Class International shipment that uses the Large Envelope or Flats package type with a contents type other than Documents is 4.4 lbs. These shipments will automatically use's Global Advantage Program labels.

More Rate Details From

To see more details on the increases from 2020 to 2021 - including Priority Mail Express and Media Mail options - please review the very thorough blog post from  New USPS Postage Rates for 2021.