ppm to molarity calculator
Enter the ppm value and the substance formula to get its molarity. Useful for water, soil and environmental lab analysis.
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How to use it
- Enter concentration and substance formula.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
In dilute water solutions 1 ppm ≈ 1 mg/L, so molarity (mol/L) = ppm ÷ (1000 × molar mass).
Example
Inputs: Concentration = 100 ppm (mg/L), Substance formula = CaCO3. Result: Molarity: 0.001 mol/L; In mmol/L: 0.999141 mmol/L; In µmol/L: 999.1407 µmol/L.
Limits and caveats
- Treats ppm as mg per liter, which holds only for dilute water solutions.
- Water reports may express hardness or nitrate as an equivalent substance; use the formula the lab used.
Questions about this tool
Is ppm always equal to mg/L?
Only approximately, for dilute water solutions whose density is close to 1 kg/L.
What molarity is 100 ppm of calcium carbonate?
CaCO3 is 100.086 g/mol, so about 0.000999 mol/L, close to 1 mmol/L.
How do I go from molarity back to ppm?
Multiply the molarity by the molar mass and then by 1000 to get mg/L.