Interesting, my old 48Sq Ft DE filter has a label which says:
"Use 1lb Coffee can per 5Sq Ft"

For the longest time I agonized over this, since I have not seen a 1lb coffee can in a long time, I'm sure they are around but I get the 2lb 2.5oz kind. Then I realized that a pound is not always equal to a pound.

What I think they want, and what dry goods normally use, is the volume equation where 1lb = 16oz =2 cups like in a household measuring cup. Now I just keep a big one and equate 2 cups (16 oz) for each 5 sq ft of filter.