I'll post this comment as answer, as I'm confident enough that what I asked is not possible.
I) Couple of similar questions trying to do the same, without success:
II) This article: Excel Pivot Table Calculated Field for example lists many restrictions of Calculated Field:
III) There is tiny limited possibility to use AVERAGE()
and similar function for a range of cells, but that applies only if Pivot table doesn't have grouped cells, which allows listing the cells as items in new group (right to "Fileds" listbox in above screenshot) and then user can calculate AVERAGE()
, referencing explicitly every item (cell), from Items listbox, as argument. Maybe it's better explained here: Calculate values in a PivotTable report
For my Pivot table it wasn't applicable because my range wasn't small enough, this option to be sane choice.