Predefined Parcels and Restrictions
USPS has nineteen predefined parcels supported by EasyPost, detailed below. Predefined parcels are an easy way to classify and therefore price a package. With the EasyPost API, pick a predefined parcel that qualifies for your shipment (and sometimes add the weight) in your request and request rates.
The chart below shows USPS Package Options Restrictions for all their major packaging options. These are the weight and dimensional limits to what USPS allows.
 Not available for international shipments.
 Only used with Parcel Select Lightweight.
 Marks package for Balloon Price.
On how this can be included with your EasyPost integration, see this guide here