Hi Wade,You need a surface (not contours) to calculate this in ArcGIS. The tool is called Add Surface Information, and for polylines it will return the 3d length (surface length) of the line. If you do not have the DEM originally used to derive the contours, you can interpolate a new DEM from the contours using the Topo to Raster tool. Otherwise, just use the original DEM the contours came from.Best,Eric