=SUMIF(A1:A10,"F",C1:C10)
or you could use sumproduct
=SUMPRODUCT((A1:A10="F")*(C1:C10))

Greetings from New Zealand
Bill K
"julie" wrote in message
...
Hello Oh Wise Ones (again!)

I think I need to use SumIf, but don't know exactly how.

In column A, I have a variety of letters and blank spaces. In column C I
have a variety of numbers and blank spaces.

I'd like a formula to calculate the sum of all numbers in column C if the
letter in column A is "F". (so if A3 and A8 and A9 are F, then the
formula
would calculate C3+ C8 + C9). There would never be a time where the text
in
column A would equal F and the corresponding cell in column C would be
blank.

If you have any ideas, I'd be delighted.

Thank you.