I have of late been getting seriously over billed when I use Fedex Pak poly bag to ship things, they get the dimensions totally out, which hasn't always been the case. I end up getting billed on dimensions that are much bigger than the package inside the Fedex Pak poly bag and hence get billed 3 to 4 times what I should be. My Fedex account manager applies a credit after investigating but maybe I could do something differently to prevent it happening in the first place because its a pita to resolved. I use Fedex Pak poly bag for lightweight lower value items especially when shipping internationally because it offers cheaper rates than shipping in your own packaging.

Any help would be appreciated.

This is all I can find on the Fedex website regarding Fedex Pak poly bag:

FedEx Pak shipments exceeding 2.5kg will be charged at FedEx International Priority rates. ** Dimensional-weight pricing is applicable for FedEx Pak shipments exceeding 940 cubic inches or 15,400 cubic centimeters in volume.

EDIT : By Fedex Pak in terms of this post I mean the Large poly bags, the soft plastic bag mailers, I have updated the post to clarify that.

Apologies for a dumb question, but can't seem to confirm this anywhere:

Are there minimum dimensions for a self-packaged FedEx shipment? In other words, what's the smallest box they'll accept (using a prepaid label from vendor, if that matters)? Maybe no practical "lower limit", but wanted to confirm before packing up the item.

TIA!