Linear inches of a cylinder

I am trying to calculate the linear inches of a cylindrical duffel bag for what else but the bloody space limitations of airlines. I can't find a formula other than the standard width+height+length for rectangular and square objects. However since it is cylindrical wouldn't it have a different formula. Any help would be lovely the dimensions of the duffel bag are 34 inches in length with a 16 inch diameter 8 inch radius.