Weighted Average in Pivot Table

I am trying to make a pivot tabs that shows me a weighted average in a calculated field but I cannot seem to get the formula right. I look at a few thread that attempted to do the same thing, but they are not working.

I calculate weighted averages using the following formula:

=SUMPRODUCT("dataarray1","dataarray2")/SUM("dataarray1")

But I cannot figure out how to do that in a calculated field.