If you have enabled "Use USPS Flat Rate boxes when appropriate" for USPS on our Carrier Settings page, we will try to package the items in your customer's order into one of the four types of flat rate boxes for Priority Mail that the USPS offers. In order for us to determine whether the items will fit, you will need to include dimensions in all your "Add to Cart" buttons by filling in the item length, width and height  in the HTMLWizard.  Since any amount of weight will still cost the same fixed amount as long as it can fit into one of their two box types, your customer can save a substantial amount in shipping costs in many circumstances.  We will compare what the package would cost based on weight to the cost of the flat rate box and return to the customer whichever rate is cheaper.

How will you know if the package qualified for a Flat Rate Box?  The order confirmation email from PayPal (as well as the order online in your PayPal account) lists your customer's selected ship service.  If they selected Priority Mail and the package did qualify, "FRB1", "FRB2" (the two regular-sized flat rate boxes), "LFRB" (the large flat rate box) or "SFRB" (the small flat rate box) will also be noted, for example, "Priority Mail (FRB1)".

What if the order consists of multiple packages?  If at least ONE of them qualified for a flat rate box, one of the above codes will be listed.