Sum of Product Multiple Columns/Multiple Sheets, Indefinite Range

I am having trouble with a rather complicated function which, due to its ambiguous wording, I can find no documentation on in searching.

I am trying to come up with a formula that will take the product of fields in 2 columns and sum them up as it goes. However, the actual number of rows will change dynamically, so I need it to perform this calculation on every row that has data.

For example. Columns A and B have data in rows 1, 2, 3 and 4, and I need to get the sum of their products, e.g.: Sum(A1*B1)+(A2*B2)+(A3*B3)+(A4*B4). However, the number of rows change dynamically, so I need the formula to perform this calculation as far down as the 65356th row.

How can I perform distinct, row based multiplications, summing each of them up in turn, with an indefinite range?

That worked amazingly.

Thanks very much Carim, for the easy fix!

OK, here it gets a bit more complicated it seems.

Do you know of any way to do a "SUMIF" type conditional function, but with the SUMPRODUCT function instead?

I have a column range and want the sum product for only those rows which contain the value "X".

DominicB,

Thank you very much for your reply.

If it is possible to get the sum of every product of two fields from each particular row in a column with SUMIF, rather that SUMPRODUCT - could you show me how such would be done?

I am very open to suggestions.

The SUMPRODUCT method you showed me (which I found elsewhere), does not seem to work with the latest OpenOffice. Perhaps I simply need to break down and get Microsoft Office.....