Question: When looking at measurements of ‘hardness’, what is the difference between Grains per Gallon (GPG) and Parts per Million (PPM)?

Answer: Both units of measurement refer to the amount of hardness in the water tested. Simply put, multiplying a GPG hardness reading by 17.1 will tell you what the hardness is in PPM and conversely, dividing a PPM hardness reading by 17.1 will yield the hardness in GPG.