Parts per Million ppm 1 liter of water 1 kg 1 mg kg =1 ppm 1mm3 liter =1 ppm 1 mg liter =1 ppm Parts per Million ppm 1 liter of water = 1 kg 1 mg / kg = 1 ppm 1mm3 / liter = 1 ppm 1 mg / liter = 1 ppm