🌡️ PPM to Molarity Calculator
Translate trace concentration measurements into molarity for stoichiometry, water quality, and environmental reporting.
Parts per million approximates mg/L for dilute aqueous systems.
Use the molar mass of the dissolved species.
Default 1.00 g/mL for water at room temperature.
Molarity
0.002567 mol/L
Solute Mass per Liter
0.15 g/L
Input Concentration
150 ppm
Approximate molality (assuming density 1.00 g/mL): 0.002567 mol/kg.
Converting 150 ppm with density 1.00 g/mL and molar mass 58.44 g/mol yields a molarity of 0.002567 mol/L.
How to Use This Calculator
Select the input format
Choose between ppm or mg/L based on how your data is reported. Both are equivalent for dilute aqueous solutions.
Enter concentration, molar mass, and density
Molar mass is required to convert mass concentration to molarity. Adjust density for non-water matrices.
Review molarity and supporting values
The calculator outputs molarity, solute mass per liter, and the original ppm for reference.
Use optional molality check
If density is 1.00 g/mL, the tool estimates molality to verify assumptions or communicate alternative units.
Formula
c = (ppm × density) / (1000 × M)
c is molarity (mol/L), density is in g/mL, ppm is parts per million (mg/kg), M is molar mass (g/mol). For water (density = 1 g/mL), this simplifies to c = ppm / (1000 × M).
Example
Calcium ion at 120 ppm in water (M = 40.08 g/mol, density = 1 g/mL): c = 120 / (1000 × 40.08) = 2.99 × 10^-3 mol/L.
Full Description
Environmental monitoring, water treatment, and trace analytical chemistry often express analyte levels in ppm or mg/L. Laboratory stoichiometry, however, is typically performed in molarity. This calculator bridges that gap with minimal data entry.
Enter the concentration, molar mass, and solution density to compute molarity. For aqueous samples the default density of 1.00 g/mL is usually sufficient. When working with brines, oils, or other non-aqueous matrices, supply the actual density to improve accuracy.
The tool also reports solute mass per liter and, for water-based solutions, a rough molality. Use the results to size reagents, convert regulatory limits into molar terms, or sanity-check analytical readings.
Frequently Asked Questions
Are ppm and mg/L always equal?
They are effectively equal for dilute aqueous solutions where density ≈ 1 g/mL. For other media, adjust density to reflect actual conditions.
Can I convert molarity back to ppm?
Yes. Multiply molarity by molar mass and 1000, then divide by density: ppm ≈ c × M × 1000 / density.
What about mass percent?
For dilute solutions, ppm = mass percent × 10^4. Convert ppm to mass percent if needed before using other tools.
Does temperature matter?
Temperature affects density. If the solution deviates noticeably from 1 g/mL, measure density at the working temperature for best accuracy.
Is molality more appropriate?
Molality is independent of temperature, but requires solution mass. When density is near 1 g/mL, molarity and molality are nearly identical at low ppm.