Some airlines & postal systems charge by the curious measure "length + width + height". 1. Is there a standard name for this measure? 2. What is the scientific/mathematical rationale for using this measure for charging? -- If there were such a mathematical rationale, I would think that it would somehow be based upon the statistics of packing many dissimilar boxes into a standard box -- e.g., a standard shipping container or a UPS truck. What do we know about the statistics of packing various numbers of differently shaped boxes into a large cubical box? I guess we could start with all items being the exact same shape (same L, same W, same H) and packing them into a large cube. Then consider 2 types of items, with different L's, W's and H's, and then vary the percentage of the 2 types of items & see what happens to the packing density. Etc. -- A related backwards problem might be that of taking a large standard cube & cutting it into smaller pieces of different L's, W's and H's. If we made "random" cuts in all three dimensions, what are the statistics of the different shapes that fall out? These shapes obviously pack perfectly.