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USPS Carrier Calculated shipping

Carrier Calculated shipping rates via USPS automatically calculates shipping costs based on USPS rates and containers. It uses package weight, dimensions, and shipping address to calculate shipping costs at checkout.

Tip: For an overview of the shipping process and our other shipping methods, visit Setting up shipping rates. For a general overview of Carrier Calculated shipping, visit Carrier Calculated shipping overview.

Before you begin

  • To use Carrier Calculated via USPS, you'll need to accurately label weight and dimensions for all products.
  • Carrier Calculated shipping via USPS is only available for domestic shipping within the United States.
  • 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 is in place to keep shipping estimates accurate, since larger orders interfere with USPS' shipping algorithm.
  • 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.
Note: USPS discontinued flat rate boxes for Priority Mail Express and Retail Ground. If you previously used flat rate boxes for these services, please 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

In the Home Menu, click Commerce, and then click Shipping.


Click Add Shipping Option.

 Select Carrier Calculated via USPS from the shipping options.

Step 2 - Select services

In the Formula tab, enable the services you'll support. With USPS, you can use:

  • USPS Priority Mail (Ships in 1 to 3 days)
  • USPS Priority Mail Express (Ships overnight)
  • USPS Retail Ground (previously called "Standard Post") (Ships in 2 to 8 days)
Note: First Class, Media Mail, and Envelope shipping rates aren't included in this integration.


Step 3 - Set a formula

USPS rates are calculated using a percentage markup and your shipping ZIP Code. If you print your own shipping labels, enable Use online prices to offer better rates.

Use online price

Check Use Online Price if you print your own shipping labels. USPS offers cheaper quotes for merchants who print their own shipping labels.


In the Markup box, enter a percentage or amount markup to charge more than the estimated cost for USPS charges. This is a useful way to cover the price of packaging, time spent shipping, or other additional costs.

Ship from ZIP Code

Enter the ZIP Code for your shipping origin. If you ship products from your home or store location, this should be your ZIP Code.

Step 4 - Add containers

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.

  • USPS recently discontinued flat rate boxes for Priority Mail Express and Retail Ground. If you previously 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.
  • You may want to visit the USPS website to reference the standard boxes they offer and then add those dimensions to the containers.

Click Add Custom Container. 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.

Click the + icon to add more containers based on the box sizes you use to ship packages.

When you're done adding containers and editing your formula, click Save.

Note: You'll see an error if your container is larger than your carrier's package size limit. To resolve this, see Shipping oversized items.

Step 5 - View USPS shipping information

To learn more about how your items are packed and the rates you're charging, view an order's shipping information.

Step 6 - Check your rates (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.

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