Louis wrote:(using the USPS Flat rate medium box (max 8 lbs) or the large box (max 12 lbs)).
In fact both the medium and the large flat rate box have an allowance of up to 20 lb. Most coffee distributors from the GCBC, and many other fellow home roasters, will readily ship up to 15 lb, of greens in a medium flat rate box ($27.95 US). Sweet Maria's will only use the large flat rate box ($37.50 US) with an 18 lbs limit.
For large shipment of greens UPS is not too bad. They will only charge $18.23 CAN for brokerage regardless of weight (at least up to 66 lb. which was my largest cross border order to date) and the base cost is much cheaper than USPS for heavy package.
I use to hate UPS and in fact will never use them for anything other than green coffee because of the brokerage charge that are just out of control. But for green coffee it seems to be simple enough that they do not gouge me blind!