USPS has strict box requirements-they will not return any of the flat-rate methods if the packing box doesn’t meet their set dimensions. Ex: Add USPS Small Flat Rate Method if you added USPS Small Flat Rate Boxįrom there, you are all set up! USPS will return the selected method when the designated box for that method is used. Navigate to the USPS carrier > Basic > Active Shipping Methods and add the corresponding shipping methods that match the boxes you intend on using.This will let you choose the flat rate boxes/envelopes which are pre-defined with the proper sizes. Note that when you define a box on the basic tab, you’ll see “Box Size” drop-down.In the boxes section, add the desired USPS Flat rate boxes/envelopes.

Ensure that dimensional packing is enabled from the features section.For USPS to return these methods, you’ll need to have your boxes configured properly and dimensional packing feature enabled in ShipperHQ. These methods, alongside envelope methods, are box size-driven methods. USPS Flat rate box methods are often used by merchants that want to show their customers fixed rates while also packing products in pre-determined box sizes. How to configure the Product Page Shipping Calculator.

Usps flat rate small box dimensions