Convert between PPM and Molarity by selecting your Conversion Direction, entering a Concentration, Molar Mass, and Solution Density — and the calculator returns your Converted Concentration, equivalent mg/L value, and the conversion formula used.
Converted Concentration
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Concentration (mg/L)
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Formula Used
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PPM (parts per million) represents the mass ratio of solute to solution (typically mg/L for dilute solutions), while molarity (M) measures the number of moles of solute per liter of solution. Molarity considers the molecular weight of the substance.
To convert ppm to molarity, use the formula: M = (ppm × ρ / 1000) / Mᵣ, where ρ is solution density (kg/L) and Mᵣ is molar mass (g/mol). For dilute aqueous solutions, ρ ≈ 1.000 kg/L.
Use custom density for concentrated solutions, non-aqueous solvents, or when working with solutions that have significantly different densities than water (1.000 kg/L). This provides more accurate conversions.
Molar mass converts between mass-based concentration (ppm) and mole-based concentration (molarity). Different substances have different molecular weights, so the same ppm value will result in different molarities.
For dilute aqueous solutions, 1 ppm approximately equals 1 mg/L. This approximation holds when the solution density is close to that of pure water (1.000 kg/L).
The water density assumption (ρ = 1.000 kg/L) is very accurate for dilute solutions (typically <1000 ppm). For more concentrated solutions, using the actual solution density improves accuracy.
Yes, use the reverse formula: ppm = (1000 × M × Mᵣ) / ρ. Enter your molarity value and the calculator will compute the equivalent ppm concentration using the same molar mass and density parameters.