Parts per million

Similar term(s): ppm.


A weight to weight ratio used to describe concentrations. Parts per million (ppm) is the number of units of mass of a contaminant per million units of total mass.

Source: GreenFacts


ppm (or ppmm) is used to measure the concentration of a contaminant in soils and sediments. In that case 1 ppm equals 1 mg of substance per kg of solid (mg/kg).

ppm (or ppmm) is also sometimes used to describe small concentrations in water, in which case 1 ppm is equivalent to 1 mg/l because a liter of water weighs approximately a 1000 g. This use of ppm tends to be phased out in favour of mg/l.

ppm (or ppmV) is often used to describe concentrations of contaminants in air (as a volume fraction). In this case the conversion of ppm to mg/m3 depends on the molecular weight of the contaminant.

For example, 1 ppm chlorine represents one part of chlorine in one million parts of air by weight, which is 1.45 mg/m3.

The ppm unit is mainly used in North America.

Source: GreenFacts

Related words:

Concentration - Contaminant(s) - Environmental media


Español: Partes por millón
Français: Parties par million

Related publications: