USPS determines if packages are subject to dimensional rates by rounding package dimensions down or up to the nearest inch.
A 12.4" x 12.4" x 12.4" package, that weighs 5 pounds, that is sent from zip code 50401 to 90001 (zone 7), would incur the following rates:
Ground Advantage Retail $19.60
Priority Mail Retail $29.20
Ground Advantage Commercial $12.73
Priority Mail Commercial $22.37
Although this package is physically larger than a cubic foot, under USPS guidelines this package is not subject to dimensional rates as USPS rounds the dimensions down to 12" x 12" x 12" for computing its volume.
The above rates are confirmed by USPS's Notice 123 Price List as well as eBay's shipping calculator tool, USPS's calculator and PirateShip's calculator - all of which accept decimal values for package dimensions.
eBay's listing form does not accept decimal values and eBay's guidelines state to round up package dimensions to the near inch, in violation of postal regulations.
eBay's software developer guidelines state to round up package dimensions to the nearest inch and only submit whole number package dimensions to eBay, in violation of postal regulations.
Under eBay's false guidelines the package mentioned above would have its dimensions rounded up to 13" x 13" x 13". Now the package is subject to dimensional rates as its volume of 2,197 square inches (13 x 13 x 13) is over a square foot. It would be subject to a dimensional rate for a 14 pound package rather than it actual weight of 5 pounds (2197 / 166 = 13.23 Rounded Up to 14). The package would now incur the higher rates below, with the rates within the brackets representing what the package should be charged using USPS guidelines.
Ground Advantage Commercial $21.11 (12.73)
Priority Mail Commercial $43.22 ($22.37)
Ground Advantage Retail $39.80 ($19.60)
Priority Mail Retail $64.55 ($29.20)
This means many buyers on eBay will be over charged for shipping as packages will be assessed higher dimensional rates when they are not subject to dimensional rates under USPS guidelines. eBay can't claim ignorance in the manner as eBay's own shipping calculator accepts decimal values and computes rates according to rounding the dimensions up or down to the nearest inch.
---
On the other hand eBay' shipping calculator tool does not properly calculate Priority Mail Cubic rates. It does not round the dimensions down to the nearest quarter inch to compute the volume of the package.
Since decimal values for package dimensions are not allowed eBay cannot correctly determine if packages are eligible for Cubic rates or calculate those rates.
This means packages will be charged for the next highest Cubic pricing tier or be considered ineligible for Cubic rates altogether as the improperly computed volume exceeds 0.5 square feet.
---
This is nothing less than wholesale fraud on eBay's part to overcharge buyers for shipping so eBay makes more FVF on shipping.
