Parts Per Million (ppm)

Definition - What does Parts Per Million (ppm) mean?

Parts per million (ppm) is a dimensionless quantity and measurement unit that is used to express a very dilute concentration level of a solvent or particulate matter in a solution, such as when describing the level of pollutants in the air, water or other fluids. Thus, parts per million refers to one item in a million of anything of the same size. It is used to express very small concentrations.

Corrosionpedia explains Parts Per Million (ppm)

Parts per million describes very minuscule values such as mass fraction or mole fraction. It represents a fraction of a whole number in units of 1/1,000,000 or

1 ppm = 10-6 = 0.0001%

For example, 1 ppm of ink in water means that in a million mass units of water there is one mass unit of ink.

Just like parts per million, concentration may also be expressed in similar units, such as:

  • Parts per billion or ppb (10-9)
  • Parts per trillion or ppt (10-12)
  • Parts per quadrillion or ppq (10-15)
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