5 or 4 can be the length. And 5 and 4 can be the width.
length: 5, 4, 2, 10, etc.
width: 5, 4, 2, 10, etc.
the numbers listed above are options. Multiply the numbers.
$${\mathtt{5}}{\mathtt{\,\times\,}}{\mathtt{4}} = {\mathtt{20}}$$
And $${\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{10}} = {\mathtt{20}}$$.
there are many more, but these are commonly used. Hope it helps!
