About this tool
Convert a concentration between parts per million (ppm) and molarity (mol/L) using the solute's molar mass and the solution density. For dilute aqueous solutions the density defaults to 1.0 g/mL. All conversions run in your browser.
Molarity is found with M = ppm × ρ / (1000 × Mr), and parts per million with ppm = M × Mr × 1000 / ρ, where ρ is the density in g/mL and Mr is the molar mass in g/mol. The tool also reports the concentration as mg/L (equal to ppm × ρ) and µg/mL, which is numerically identical to mg/L.
Choose whether you are solving for molarity or ppm, enter the known value, the molar mass and the density, and the result updates instantly. This is handy for lab dilutions, water-quality figures and dosing calculations.
Frequently asked questions
How are ppm and molarity related?
They are linked through molar mass and density: M = ppm × ρ / (1000 × Mr). Rearranged, ppm = M × Mr × 1000 / ρ, where ρ is g/mL and Mr is g/mol.
Why does density matter?
Parts per million is a mass ratio (mg per kg of solution) while molarity is per litre of solution, so the density converts between mass and volume. For dilute water-based solutions ρ ≈ 1.0 g/mL and ppm is very close to mg/L.
Is ppm the same as mg/L?
At a density of 1.0 g/mL they are equal. More generally mg/L = ppm × ρ, and µg/mL is numerically the same as mg/L, so all three describe the same concentration in different units.
Does anything get uploaded?
No. The conversion is a small formula that runs entirely in your browser, so the values you enter stay on your device.