Ebay USPS Cobranded Flat Rate Priority Mail Boxes

[munakatakun]

Did I miss something?  In my quest to use these boxes to mail my packages on eBay, I have been through

1. The Cobranded boxes order page http://ebaysupplies.usps.com/
2. Ebay help.
3. The Print Shipping Label page on paypal's domain

Nowhere on any of these pages does it explain the congruency between the box dimensions, of which there are six (6), and the adjectives used interchangeably to describe their size (most notably on the final selection page), small, medium, and large.

Now why the **bleep** is that?  How does one make the proper calculation for shipping?  If all of these pages are linked, then why isn't there a menu where I can put in either the  Item Number, Dimensions, or any of the codes printed on these boxes, which are all apparently useless.  The smallest volume box is obviously small (logically speaking).

What size is a shoebox?

[munakatakun]

So, if I select package for those boxes which are not Flat Rate, I should be able to input the dimensions of those boxes, but the text box doesn't even allow enough characters to input the correct dimensions!!!  It's asinine.

[da1013]

Rounding up the dimensions may help? One of the USPS boxes measuring 12.125" x 13.375" x 2.75"  would then be 13 x 14  x 3.