Free · Concentration conversions

Mass-Fraction PPM & Solution Concentration

Relate mass-fraction ppm, mg/L and molarity using solution density and solute molar mass.

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Edit a calculated value to solve backwards, or lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

At a solution density of 1,000 kg/m³, 58.44 mg/L is 58.44 mass-fraction ppm. With a solute molar mass of 58.44 g/mol, that concentration is 0.001 mol/L.

ppm by mass = (mg/L) × 1000 ÷ solution density in kg/m³; mg/L = mol/L × molar mass in g/mol × 1000

Worked example

Enter these known values and leave the other values blank.

Solution density
1000 kg/m³
Solute molar mass
58.44 g/mol
Molar concentration
0.001 M
PPM by mass
58.44 ppm
Mass concentration (mg/L)
58.44 mg/L

Assumptions and limitations

  • Density is the density of the entire solution at the relevant conditions, not the density of the pure solute. Mass-fraction ppm means milligrams of solute per kilogram of solution.
  • The numerical equality of ppm and mg/L holds when solution density is exactly 1 kg/L. It is only an approximation for dilute water-like solutions and does not apply to gas volume fractions.
  • Enter positive concentrations, density and molar mass. Match the molar mass to the actual chemical species; this tool does not determine composition or reaction yield.

Common questions

Why do ppm and mg/L differ for dense solutions?

ppm by mass uses kilograms of solution in the denominator; mg/L uses litres. At 1,200 kg/m³, 60 mg/L corresponds to 50 mg/kg, or 50 ppm by mass.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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