Parts Per Million Concentration

Definition

A mass-over-mass ratio expressing one part of solute per one million parts of water, treated as equivalent to mg/L in dilute aqueous solutions.

Because one liter of water weighs very close to one million mg under normal conditions, 1 ppm is approximately 1 mg/L or 1 mg/kg. This equivalence is excellent for dilute solutions but becomes less exact as concentration rises and density departs from that of pure water. In water treatment, ppm should almost always be treated as mass over mass rather than volume based.

Related concepts

Dissolved Solids · Added Substance Calculation · Percent to ppm Conversion

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Part of The Blueprint of Water · 📏 measurement