It’s a difficult conversion but the correct answer is almost always 1. (Unless you’re using heavy water instead of RODI.). Then relativity takes hold and physics calculations must be performed to take into account particle deterioration rates, not to mention evaporation at STP. According to Einstein it’s really easy but I blindly trust Hanna and pray that my syringe is properly calibrated.
But the million dollar question is do any of us really know the salinity of our tanks.