since the number of 'charms, strips, layers' vary depending on the collection it varies---but jelly rolls are 2 1/2" strips by width of fabric- (so 40"-42" long) one yard is 36" ---14 strips = 35 inches. (a jelly roll that has 40 strips = 100" of fabric- or 2 3/4 yards.)
I've purchased charm packs that had 25 fabrics- and ones that had 56 fabrics....again it varies---a charm is 5" square- so, 7 across = 35 inches...8 up = 40 inches... (7x8) = 56 charms a yard
layer cakes--10" squares= 4 up (40") 3 across (30") 12 in a yard.