When using REST API, each service has a unique identifier (SKU). There are thousands of available SKUs – you can limit the number of services displayed in your checkout by selecting specific values for Type, Sub type, Shape and Delivery type fields. For a detailed information on SKUs please see the USPS User SKU Guide.
REST API Services
Type
This code designates a specific category within the overall USPS service. In other words, once you’ve identified the general service (Domestic or International), the Type code pinpoints which product variant or service offering is being used. It helps differentiate products within the same service family. It also determine what is the meaning of the remainder of the SKU.
Sub-Type
The Sub-Type code adds an extra layer of granularity to the product or service. It refines the classification provided by the Type code by specifying further processing or handling characteristics—such as whether an item is processed using automation, whether it follows a carrier route, if it’s considered nonmachinable, and so on. This ensures that even subtle differences in service attributes (like presorting or special handling) are captured.
Shape
The Shape code is used by specific mail classes (First-Class Mail International, First-Class Mail, Marketing Mail, USPS Ground Advantage, Parcel Select, and Bound Printed Matter) to indicate the physical form of the item being mailed. The shape directly affects pricing and handling rules. For example, the code will distinguish if the item is an envelope, a box, a bag, or another form (like a postcard or a flat). This is important because the dimensions and form factor can change the postage rate.
Delivery Type
The Delivery Type component (used primarily for certain Parcel Select SKUs) further distinguishes items based on specific delivery attributes. It includes additional delivery instructions such as “Hold for Pickup” or “Sunday/Holiday” delivery. This allows for precise pricing and service rules based on the handling and delivery conditions of the package.
Each of these components—Type, Sub-Type, Shape, and Delivery Type—works together to create a detailed descriptor (SKU) that maps directly to the appropriate pricing and service level for a given USPS mailing product. This system ensures that every factor, from the physical shape of the item to the special delivery conditions, is accounted for in the postage calculation.
Matching proper SKU
In order to properly match the SKU for the certain USPS service, firstly, you should review the USPS documentation mentioned at the very beginning. What is crucial is that, you should identify the proper USPS service in the SKU documentation and look for the Type, Sub-Type, Shape and Delivery Type which are associated with it – they are indicated by the letters.
Furthermore, it is worth to launch the Debug Mode, where you will find the buttons like “Show matched SKU” and “Show unmatched SKU”. By clicking mentioned buttons, you will see what SKU has been properly matched and which not. Above you can find the example, where for the USPS Ground Advantage you can see two properly matched SKU – Service subtype and Delivery type. This means that the Service type and Shape should be adjusted.