Area of 20, 24, and 36 exp cassettes?

I've seen this somewhere before, but I don't know where! My fixer gives its capacity in square inches per liter, rather than number of cassettes. This makes sense, since most of us shoot both 24 and 36, or load our own to custom lengths. Anyone have a handy square inches per cassette figure? Or should I measure the length and width of typical cassettes, and disregard the area lost in the perforations.

Thanks!

36 EXPOSURES is about 8x10 inches.

Thanks, ic-racer! Makes sense, since one can contact print 36 exp on an 8x10 sheet, with care.