Shipping - What is an irregular package?

[thatgirlgoodbuys]

I am learning to put information into calculated shipping.  I am using 9 X 12 poly mailers.  I then enter the weight.  Below this, it has a box to check for an irregular package.  How do I know if I have an irregular package?  Does having an irregular package add to the cost?  Thanks for your help.

[wooden_flower · Accepted solution]

There is a list of what is considered an irregular package here -

https://www.ebay.com/help/selling/shipping-items/usps-ups-package-types?id=4864

Some would incur additional costs, some do not.