Cross Table Multiplication Query

I am currently building a website to deal with different product information and sales with php. I am using SQL to sort the database and pull out information.

The final thing i need to do is work out the total revenue of each product however the problem i am having is that the 'Price' column and 'SalesVolume' column are in two different tables and they need to be multiplied together.

The two tables and column headings are as follows:

Product
ID
Name
Price

MonthlySales
ID
ProductCode
Month
Year
SalesVolume

(ID and ProductCode are linked together in a relationship)

I cannot see anything wrong with the syntax in my query however i believe there is.

Here is the query I am using:

Code:
"SELECT SUM(Products.Price * SUM(MonthlySales.SalesVolume)) as revenue FROM Products
INNER JOIN MonthlySales ON(Products.ProductCode = MonthlySales.id) GROUP BY Products.ProductCode";