The circumference of a cylinder works the same way as the circumference of a circle, as both faces of a cylinder are circles.
The circumference of a circle can be found with the formula [tex]C=2 \pi r^{2} [/tex] where r is the radius.
If you can enter the answer in terms of pi, I would suggest you do that. If not, just multiply by 3.14.
Hope this helps!
-refrac532