As you build your pivot table reports with the PivotTable Wizard, Excel is busily adding fields and performing calculations in the background.
The wizard is designed to always sum numeric data and to always count text data. The wizard allows you to produce a standard pivot table in a few seconds. However, sometimes the PivotTable Wizard doesn't quite hit the mark.
A common problem is that Excel chooses to count data that you wanted summed. This can happen when your numeric data inadvertently contains a single blank or text cell mixed in.
Sometimes, you want to create something other than the default pivot table. In addition to Sum and Count, Excel offers a total of 11 subtotal options that can be used separately or in combination. You can combine these with nine different running total options. That makes for 5,621 different ways to present each data field in the pivot table.
You can step in and take control of the calculations by customizing the pivot table. Customizations are controlled in the PivotTable Field dialog box.