OUCH, that size will be extremely costly since PO rolled out DIM (dimension) weight charges in 2018. I dont think Bonz allows for dimensions put in for larger boxes (at least I havnt see it). They have an option for large boxes but dont know what they use for the dimensions of a box.

I stopped selling things that would go in a large box because it cost more than the items now.
You can get a ballpark figure of costs on the USPS site but it also depends on distance (zip) so you got to checkout all zones and maybe take an average. Bonanza only calculates Priority rates (I have been asking for YEARS that they also allow for Parcel because it is a bit cheaper) and it falls on deaf ears here.

We’ve found using pirateship.com for our labels to be most useful. Don’t waste a second calling one of the carriers for a quote – that’d be absurd.

thanks everyone

For a box of that size, you might find UPS or FedEx offer better rates than USPS. It’s going to be very expensive whichever way you do it, however. Makes a huge difference once you go over the 12×12×12 volume…