How this calculator works
Mass fraction times solution density gives solute mass per volume. Divide by solute molar mass to obtain molarity. The density must describe the solution at its working temperature and concentration, not the pure solute. Preset formulas determine molar mass from IUPAC 2021 weights; they do not supply a concentration-dependent density. In molar-mass mode, the measured percentage, density and molarity determine the mass independently of the preset.
Formula
c(mol/L) = 1000 x density(g/mL) x mass fraction / M(g/mol). Equivalently c = 10 x density(g/mL) x percentage / M.
Worked example
A 10% by mass solution of a 100 g/mol solute at density 1 g/mL is 1 mol/L. At the same density and molar mass, 0.5 mol/L is 5% by mass.
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Frequently asked questions
Can I use a w/v percentage?
Use the percent solution tool or divide grams per litre by molar mass; solution density is unnecessary for that basis.
Does a preset include density?
No. Density changes with temperature and composition, so enter a suitable measured value.
Why specify the solute formula?
A hydrate, salt or different chemical form can have a different molar mass.