I am working in Excel 365 Online and have a pivot table. The Pivot table contains columns of various pack sizes for different types of products. that is sourced from one column of the data table. I need to display a column that calculates these different pack sizes expressed as Gallons.

I see options how to do this in the desktop version but I cannot seem to figure out how to do it via Excel 365 Online. Does anyone have any suggestions or insight for me?

Thank you