=sumif(b5:b317,criteria,c5:c17)

Check also sumproduct() for more complicated structures

=sumproduct(--(and(b5:b317=criteria1,b5:b317=criterian2)),--(c5:c3170.5),c5:c317)
as an example

"EJ" wrote:

I've been using =SUMIF(C$5:C$317,"0.5") - column C can contain any value
between 1 and 50 or text and I need the sum of any numerical values, but I
only need it to use this if cells in column B meet a particular criteria.