You can use carrier predefined package rates. In this case, a shipping fee will be calculated based on that specific package for a carrier.
Predefined rate packaging is supplied by your carrier. Its shipping cost is not determined by the weight of your shipment. If you are using Omnibasis Easypost.com integration, you can find the names for predefined package rates from Easypost website. Navigate here to https://www.easypost.com/docs/api#predefined-packages Predefined Packages section to find the names of predefined packages.
For example, for USPS the names are
For FedEx are
For UPS are