If you take a raw pic at full scale as jpg, it should be the same size X wise as the raw. Take a raw pic and save to jpg, look at it's details, then take another raw as raw and use that X. Should work? Raw may add a few pixels to each side as well (black framing pixels). So you may need to add a few for that as well, as most processing systems will chop those off. Smarter systems use those black areas to adjust for or detect noise levels in the raw image.