The formula for the volume of a cylinder is

V = (pi)r^2 * h

where r is the radius of the end-cap and h is the height (or length) of the cylinder.

If you roll your paper along its length (which I would take as the larger of the two dimensions) then the circumference of the end-cap will be 44 cm. Thus:

C = 2(pi)r

and you can find r. The height of your cylinder would then be the other dimension of the paper, 18 cm.

-Dan