Finished block measurements????

I know we should all know the answer to this question but I will put it out there anyway.
If you are told to make a 12 1/2 by 12 1/2 inch block the block should measure 12 1/2 when you mail them out correct?
I am on a couple of different sites some people ask for 12 1/2 finished or 12 finished if it says 12 are they really looking for 11 1/2 or 12 1/2 that when put into a sash or sewn together they sew down to 12???