Analytical · Free Calculator
ppm to Molarity Calculator
Convert between mass concentration (mg/L or ppm in water) and molar concentration (mol/L) using the molar mass of the substance.
mg/L to mol/Lmol/L to mg/LMolar massDilute solutions
g/mol
mg/L
Molarity0.008556 mol/L
Molarity8.556 mmol/L
How this result was calculated
- mol/L = mg/L ÷ (molar mass × 1000) = 500 ÷ (58.44 × 1000) = 0.008556 mol/L
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Mass and Molar Concentration
c (mol/L) = ρ (mg/L) ÷ (M × 1000)
ρ (mg/L) = c (mol/L) × M × 1000
ρ (mg/L) = c (mol/L) × M × 1000
M is molar mass in g/mol. In dilute aqueous solutions 1 mg/L ≈ 1 ppm by mass because 1 L of water weighs about 1 kg.
Worked example
500 mg/L of sodium chloride is 500 ÷ (58.44 × 1000) = 8.56 mmol/L.
Key insight: ppm equals mg/L only for dilute water based solutions. For dense liquids or concentrated solutions, divide by the solution density to get true ppm by mass.
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Frequently Asked Questions
How do I convert ppm to molarity?
Divide mg/L by the molar mass in g/mol and by 1000.
Is ppm the same as mg/L?
Approximately, for dilute solutions in water with a density close to 1 kg/L.
What is the molar mass of NaCl?
58.44 g/mol (sodium 22.99 plus chlorine 35.45).
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