Perimeter
Returns the geographic perimeter of a geometry object.
Option Name  Description 

Distance units  Specifies the unit of measurement to use to calculate the perimeter. One of the following:

Geometry field  The name of the field that contains the geometry whose perimeter you want to calculate. This field also accepts geometries that are generated by stages in the Enterprise Routing Module, such as a LineString or Polygon. 
Length field  The name of the field that you want to contain the perimeter length returned by Spatial Calculator. 