Explanation:
come on ! you know that.
for a volume we need to multiply 3 pieces of dimension information (kind of length, width and height, whatever makes sense for a shape, but it always has something to do with left-right, front-back, up-down).
as for an area we need to multiply only 2 pieces of dimension information.
and for a length, line, distance, ... we need only one piece of dimension information. and therefore no multiplication.
so, of course,
length × width × height
is correct.