Parts Per Million (Ppm)

Unit weight of solute per million unit weights of solution (solute plus solvent), corresponding to weight-percent except that the basis is a million instead of a hundred. The results of standard API titrations of chloride, hardness, etc. are correctly expressed in milligrams (mg) of unknown per liter but not in ppm. At low concentrations, mg/l is about numerically equal to ppm. A correction for the solution specific gravity or density in g/ml must be made as follows:

Thus, 316,000 mg/l salt is commonly called 316,000 ppm or 31,6% , which correctly should be 264,000 ppm and 26.4% respectively.