I've noticed Amazon.com shipments come in boxes with numbers, like C2 or Z3, corresponding with the container's dimensions. I haven't found a comprehensive table or data on which is which, however — my searches have yielded too much noise.
It is convenient to have some Amazon.com boxes (and packing materials) laying around if you need to ship stuff back out. Especially because packing materials can cost a fair amount. Just be careful with the labels and peel 'em off nice 'n' smooth, and you're good to go.