Parts per million

Parts per million (abbreviated "ppm") is a measure of solution concentration. It is defined as the mass of the solute (solution component) of interest, divided by the mass of the entire solution, and multiplied by <math>10^6</math>.

Parts per million is a ratio of masses, not volumes, and is technically dimensionless. Approximate conversion from ppm to grams per liter is sometimes used for aqueous solutions, using the assumption 1 liter water masses 1000g under standard conditions.

1 ppm =

    = 0.0001% by mass 
    = 0.001 g/L