How to use pivot table to get a value by multiplying two different datas

[phs90]

Hi everyone. I am now working on how to use pivot table calculate revenue (by multiplying volume and price) of the company. For now, I have combine two data sheets which are volume sheet and price sheet and hence create a pivot table. But at the column field there it can only show volume or price of the year. Even the value field settings only have sum, count, average... but do not have product (multiply function) How do I make the column field to have revenue of the year?

Thanks a lot.