You will further get a list of options just click on Calculated Item. How To Insert A Calculated Items In Pivot Table Just click on any of the items in your pivot table. Click on the Analyze then on Fields Items Sets.
Then in the dropdown list you select of Grand Total.
Steps to create calculated Item in pivot table. In the Create PivotTable dialog box tick Existing Worksheet. In the dialog box select the tab Show Values As. On the Analyze tab in the Calculations group click Fields Items Sets and then click Calculated Field.