To add a formula (Calculated Field) as a new column in a PivotTable report:
1. Select a cell in the PivotTable report.
2. Press Alt+P to select PivotTable dropdown icon from Pivot Table toolbar, select Formulas, and then Calculated Field.
3. In the Insert Calculated Field dialog box, type the formula name in the Name box.
4. In the Fields list box, select the first field name to insert and click Insert Field. The field name is copied into the Formula box.
5. Type / (in this example), repeat step 4 to insert the second field into the formula, and then click OK.
6. To format the new field, select a cell in the field and click the Field Settings icon on the PivotTable toolbar.
CAUTION!
This option can some times return incorrect calculation results when using multiplying or dividing.
Screenshot // PivotTable report - Adding a Calculated Field
