The Calculate Length activity calculates the length of the input geometry.
You may need to calculate the length or perimeter of a geometry. You could take the geometry from a parcel feature and calculate its perimeter to estimate the length of a fence.
Geometry  | 
Required Type: esri.Geometry (3.x, 4.x)* The input geometry whose length is to be calculated.  | 
Geodesic  | 
Optional Type: Boolean Determines whether the length to be calculated is geodesic. If not, the planar length is returned. The default is false. Note: geodesic only works with WGS84 (wkid: 4326) and Web Mercator spatial references.  | 
Unit  | 
Optional The measurement unit of the return value. Defaults to the units of the input geometry. Known values: meters | feet | kilometers | miles | nautical-miles | yards.  | 
* VertiGIS Studio Workflow uses different versions of Esri's ArcGIS API for JavaScript depending on the type of host application. See Underlying Technologies for information.
length  | 
Type: Number The calculated length.  | 
For information about the ID, Display Name, and Description properties, see Properties Common to all Activities.
This activity works when the device has intermittent connectivity to the network.
Supported from: Geocortex Viewer for HTML5 2.9, ArcGIS Web AppBuilder 2.4.
See also...
https://developers.arcgis.com/javascript/latest/api-reference/esri-geometry-Geometry.html