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USPS Carrier Calculated shipping

Carrier Calculated shipping rates via USPS automatically calculates shipping costs based on USPS rates and package dimensions. 

Tip: For an overview of all shipping options, visit Setting up shipping rates.

Before you begin

  • To use Carrier Calculated via USPS, you'll need to accurately add weight and dimensions for all products.
  • Carrier Calculated shipping via USPS is only available for domestic shipping within the United States.
  • Carrier Calculated shipping is available on the Advanced plan, and certain legacy billing plans.
  • You can also set up Carrier Calculated rates with FedEx and UPS.
  • If USPS Carrier Calculated shipping is enabled, the item limit in shopping carts reduces to 150 items. (The default limit is 500 items.) This limit keeps shipping estimates accurate, since larger orders interfere with USPS' shipping calculator.
Note: USPS discontinued flat-rate boxes for Priority Mail Express and Retail Ground. If you used flat-rate boxes for these services, you can create custom containers. If you have USPS Carrier Calculated shipping and only flat-rate boxes, USPS may overcharge your customers.

Step 1 - Add Carrier Calculated rates via USPS

To set up USPS Carrier Calculated Shipping:

  1. In the Home Menu, click Settings, and then click Shipping.


  1. Click Add Shipping Option.

  1.  Select Carrier Calculated via USPS.

  1. In the Formula tab, select the services you'll support. You can use:
  • USPS Priority Mail - Ships in 1 to 3 days
  • USPS Priority Mail Express - Ships overnight
  • USPS Retail Ground - Ships in 2 to 8 days. (Previously called "Standard Post")
Note: First Class, Media Mail, and Envelope shipping rates aren't included in this integration.

  1. If you print your own shipping labels, check Use Online Price. USPS offers cheaper quotes if you print your own shipping labels.
  2. To charge more than the estimated cost for USPS chargers, you can enter a percentage markup in the Markup box. This is a useful way to cover the price of packaging, time spent shipping, or other costs.
  3. Enter the zip code for your shipping origin. If you ship products from your home or store location, this should be your zip code.
  4. Click the Containers tab to list your available shipping containers (boxes or packages) for the service type. Squarespace estimates shipping costs based on the minimum number of packages and smallest containers possible.

Important notes about containers:

  • USPS recently discontinued flat rate boxes for Priority Mail Express and Retail Ground. If you used flat rate boxes for these services, create custom containers instead.
  • Since customers may purchase multiple items, it's important to set containers larger than your product dimensions. If your containers are set to accommodate one item each, this packages large orders in multiple containers and significantly increases shipping costs.
  • Visit the USPS website to reference the standard boxes they offer and then add those dimensions to the containers.
  1. Click Add Custom Container.
  2. A sample container will appear. Click Custom Box to edit the name, and then click on a number in the Dimensions column to enter dimensions.
  3. Click the + icon to add more containers based on the box sizes you use to ship packages.
  4. Click Save.
Note: You'll see an error if your container is larger than your carrier's package size limit. To fix the issue, see Shipping oversized items.

Check your rates and shipping information (optional)

USPS calculates rates based on the dimensions and weight of the package and the distance shipped. To test how rates for different product combinations are calculated, run test orders.

Running a test order will show you how items are being placed in their containers. If the rates seem high, you can check them against the USPS calculator. You can often reduce rates by creating a custom container or reducing the dimensions of a product so it fits the container better.

To see how shipping rates and packages are calculated for a real order, view the order's shipping information.

Tip: If you run a test order and have questions about how the USPS shipping price was calculated, open a ticket with the following information:

  • Exact products in the cart
  • Shipping options selected
  • Exact address used
  • Order # for any relevant test orders


“Some of your products are too large to be shipped via one of your shipping options”

This yellow warning displays when the dimensions of a product exceed the package sizes offered by USPS. USPS provides information on sizes and weights for oversized items here.

To resolve this, add another shipping rule for oversized items using Depending on Weight or Flat Rate shipping methods.

If you add an item to your store over these limits, you'll see a warning message in the product editor.

If all items in a customer’s order are oversized, USPS won't be available as a shipping option.

If both a regular and oversized item are added to an order, customers can select a USPS shipping method; however, the oversized item won't be included in that calculation.

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USPS Carrier Calculated shipping