Mass percent by weight alone cannot determine molarity. Supply the density of the full solution and the solute molar mass so the calculator can relate one liter of solution to solute moles.

Formula: solution g/L = density g/mL × 1,000; solute g/L = solution g/L × w/w % ÷ 100; mol/L = solute g/L ÷ molar mass g/mol

Worked example

At 10% w/w, solution density 1.05 g/mL and solute molar mass 58.44 g/mol, one liter of solution has 105 g solute, or about 1.796 mol/L.

Both percent and density have defined bases

Mass percent w/w means solute mass divided by total solution mass, times 100. Density here is total solution mass per unit solution volume, at the same temperature and composition. OpenStax explains both concentration forms and their relationship through density.

One liter is an accounting basis

The calculation imagines one liter of the specified solution, finds its total mass from density, then takes the stated mass fraction as solute. Dividing by solute molar mass supplies moles per liter. It does not assume that solvent and solute volumes add.

Check the chemical identity

The molar mass must belong to the solute represented by the weight percentage. Hydrates, mixtures and ambiguous product labels can change the correct basis. This is concentration arithmetic, not a preparation or safety procedure.

Explore the related calculation

For a different starting point, try the molarity calculator or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

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