Hello doublest -
Apologies if that last response was unclear. I referenced the USPS site so you could see how they want the measurements for a cylindrical parcel. In your initial query you refer to the circumference of the cylinder, whereas the USPS site shows the diameter. If you use the dimensions as shown there and select Package as the parcel type, you can use those dimensions to acquire your label. You would use the weight, the length and the height and width measures would both be the diameter of the cylinder.