Convert concentrations without the headache. In water mode this free ppm converter turns ppm into mg/L, ppb, µg/L, g/L, % and molarity; in air mode it converts gas ppm to mg/m³ using molecular weight. Built by a team that runs an accredited water and environmental testing lab.
Concentration conversion formulas
Worked examples
- Water hardness of 250 mg/L as CaCO₃ is 250 ppm, 0.025% and 250 ÷ 1000 ÷ 100.09 = 2.50 mmol/L.
- 50 ppm of carbon monoxide (MW 28.01) at 25 °C is 50 × 28.01 ÷ 24.45 = 57.3 mg/m³.
The water conversions assume a dilute aqueous solution with a density of 1 kg/L, which is accurate for drinking water and most environmental samples. For brines, acids or soils, ppm by mass (mg/kg) and mg/L differ by the density.
Frequently asked questions
Is ppm the same as mg/L?
For dilute water solutions, yes: 1 litre of water weighs about 1 kg, so 1 mg/L ≈ 1 mg/kg = 1 ppm. For dense liquids they differ by the density.
How do I convert ppm to molarity?
Divide ppm (mg/L) by 1000 to get g/L, then divide by the molar mass in g/mol. Type the formula and the calculator works out the molar mass.
How do I convert ppm to mg/m³ for gases?
mg/m³ = ppm × molecular weight ÷ 24.45 at 25 °C and 1 atm. Use air mode and enter the gas formula.
How do I convert percent to ppm?
Multiply by 10,000: 0.5% = 5,000 ppm.
Related tools
Free educational tool by HawkInc. Results are calculated in your browser and rounded for display; check critical work by hand or with a second method.