Grid resolution and terrain analysis

[nolumanyanocamagu]

Hi there! 

I want to calculate the ideal grid size for a contours_area.shp layer. 

I will use one of Hengl's formula for calculating grid resolution.

To get the grid resolution the area Hengl's formula states that I should divide the total size of the study area and
the total cumulative length of all digitized contours.

How do I determine the total cumulative length of all digitized contours? 

[XanderBakker]

You mention you have a shapefile (contours_area.shp). If would be better to import the shapefile into a file geodatabase. When you import it into a FGDB the system will automatically manage a field called Shape_Length. You can use simple field statistics to obtain the sum of all the lengths. If you don't want to or cannot load your shapefile into a FGDB, you can use Add Geometry Attributes—Help | ArcGIS Desktop