The Calculate Geometry tool is occasionally disabled for fields that are joined to a feature class from a table. This is due to the fact that a table does not have geographic features in the map that can be used to calculate geometry from; it does not have geographic properties. The original feature class fields can still have their geometry calculated as long as they are not one of the system-managed fields (ObjectID, Shape_Length, Shape_Area, etc.). If one of the fields from the joined table requires the geometry to be calculated, the feature class should be exported, after the join was successfully established, to a new feature class so that the join is made permanent and those fields are associated with the appropriate geographic features.
The following steps can be used to join a table to a feature class, export it to make the join permanent, and calculate geometry on a field:
Note: Calculations can be made without being in an editing session, however in that case, there is no way to undo the results.
Note: Geometric calculations can only be performed on attribute tables.
Note: Different properties are available depending on the type of layer used.
Note: If calculating into a text field, adding an abbreviation for units to the calculation can be chosen. For instance, '47.5673 sq m' is an example of the output of area calculated into a text field with the units abbreviation.
Warning: Field calculation can't be undone when performed outside an edit session.