You can display shipping rates in your checkout that are calculated by USPS.
After you connect an USPS account, USPS commercial rates are shown at checkout by default. USPS commercial rates are less expensive than the retail rates and the labels need to be purchased online. If you want to display the more expensive rates, then you can activate the retail rates when you add USPS calculated rates.
Requirements for activating calculated shipping with USPS
To activate calculated shipping with USPS, you need to meet the following requirements:
Your store needs to be on the Advanced Shopify or Plus plan. If you're on the Shopify plan, then you can add this feature for a monthly fee or switch from monthly to yearly billing. For more information, contact Shopify Support.
Your store needs to have a fulfillment location based in the United States.
In the Carrier accounts section, add USPS as a shipping carrier:
If you don't have any shipping carrier accounts added, then click Connect carrier account, and then click Connect account next to USPS.
If you already have a shipping carrier account added, then click Manage carriers, and then click Connect account next to USPS.
In the Connect USPS dialog, select USPS commercial rates or USPS retail rates.
Click Save.
Step 2: Test your carrier-calculated shipping rates
After you connect your third-party shipping carrier to your Shopify admin, you can test your account integration and preview calculated shipping rates for specific package types, sizes, and destinations within the Shopify admin.
The shipping rates that are displayed during testing are sample rates and might be different from the shipping rates displayed to your customers at checkout.