How can I automatically set USPS service based on an order's weight?

One of the most common uses for automation rules in ShipStation is to automatically set the shipping service and package type based on the weight of the order, which allows you to ensure the service and package type selected are appropriate for what you're shipping.

This is especially important for USPS shipments, which have strict weight limits based on the service and package type you're using. For example, a USPS First Class Letter shipment cannot be over 3.5 ounces.

Below are some examples of automation rules that set USPS services based on weight:

Weight Example Rule under 16 oz

This rule will locate any domestic orders with a weight less than 16 oz, and set the shipping service / package type to USPS First Class Mail / Package.

Set the criteria so Country includes the United States and the Order Weight is Less Than orEqual To 16 ounces. Then, set the action to apply the service and package type you wish to apply to these shipments.

Criteria 1: country = United States. 2: Total Weight = Less Than 16oz.

USPS First Class Mail Package is generally the cheapest USPS postage option that includes tracking, so this rule can be used to select that service and package type for any orders that qualify.

Note

This rule is designed with Stamps.com in mind, which has a maximum weight of 15.99 oz for USPS First Class Mail shipments.

Endicia has a maximum weight of 15.9 oz instead, so if you use Endicia you'll need to change the Total Weight criteria to Is Less Than or Equal To 15.9 oz.

Weight Example Rule under 3.5oz

This rule will locate any domestic orders with a weight of 3.5 oz or less, and set the shipping service / package type to USPS First Class Mail / Letter.

Set the criteria so Country includes the United States and the Order Weight is Less Than orEqual To 3.5 ounces. Then, set the action to apply the service and package type you wish to apply to these shipments.

Automation Rules. Example for using Letter package.

USPS First Class Mail Letter is the cheapest available option for USPS postage, so this rule can be used to select that service and package type for your smaller, lightweight orders.

Weights with Decimals

If you're having trouble entering a decimal weight into the Total Weight criteria, type the value in a text box (such as the Search box in your browser) then use right-click to Copy and Paste to enter the value.

Weight Example Rule over 16 oz

This rule will locate any domestic orders with a weight of 16 oz or more, and set the shipping service / package type to USPS Priority Mail / Package.

Set the criteria so Country includes the United States and the Order Weight is Greater Than orEqual To 16 ounces. Then, set the action to apply the service and package type you wish to apply to these shipments.

Automation Rules. Example for Priority shipping

USPS First Class Mail is a popular shipping service for most sellers but has a maximum weight of 16 oz. This rule would switch the service to USPS Priority Mail when an order is over the maximum weight limit for USPS First Class Mail.