What logic do you use?
Currently I use UPS and USPS online tools via silent post to calculate shipping. Send them a width, height, depth, shipping method, they return a price.
The problem comes in when someone orders multiple items. Initially just to get the thing rolling what I did was find the longest sides of the items and add the heights. This overshot a little, but worked.
I'm sure you all see what *I* saw the potential for, but never expected the outstanding success of the site in question. We're getting some LARGE orders, multiple items, and it's blowing my "calculator" out of the water. When someone orders 70 12" X 2" X 1" items, you now have a box 12" X 2" X 70" high which throws ANY calculator into oversize.
So what logic do you follow? Calc the total volume, grab the largest length and width and make the height whatever's required to equal the volume?
I will cross-post this in Ecommerce because it may be more relevant there, but am interested in a programmer's point of view. 'Cause that's what I have to figure out, how to program it. :-)