Convert mass percent to molarity
The percentage concentration to molarity calculator converts percent by mass (% w/w) into moles per litre using solution density and solute molar mass. It can also reverse the relationship. Choose the direction first so the workspace requests only the concentration value needed for that conversion.
A 5% w/w solution contains 5 g of solute per 100 g of solution. If density is 1 kg/L, one litre of solution has a mass of 1000 g and contains 50 g solute. Dividing 50 g/L by a molar mass of 58.44 g/mol gives about 0.856 mol/L.
Follow the density and molar mass units
With density in kg/L, grams of solute per litre equal mass percent times density times 10. Molarity then equals that mass concentration divided by molar mass in g/mol. The reverse path multiplies molarity by molar mass and divides by density times 10 to recover % w/w.
Use the density of the final solution at the relevant temperature, not pure solvent density unless that approximation is intended. Use the molar mass of the exact solute form, including hydration or salt form where applicable. Purity or assay must be handled separately if the measured material is not the stated pure solute.
Do not combine different percentage definitions
Percent by mass is not the same as grams per 100 mL (% m/v) or millilitres per 100 mL (% v/v). A density is needed here precisely because the denominator changes from solution mass to solution volume. If a label already states g/100 mL, use the mass/volume definition instead of treating it as w/w.
The result keeps % w/w beside the percentage and mol/L beside molarity. If a reverse calculation produces more than 100% by mass, the entered molarity, density, molar mass, or concentration basis conflicts and is rejected rather than displayed as a plausible mixture.
Check the conversion in two stages
First review the displayed grams of solute per litre. Then divide by molar mass to obtain molarity. Multiplying the final molarity by molar mass should recover the mass concentration; converting that value with density should recover the starting percentage. These staged checks help locate a density or factor-of-1000 error.
The conversion is arithmetic and does not model volume contraction, reaction, dissociation, non-ideal activity, or temperature dependence beyond the supplied density. Molarity itself can change with temperature because the litre is a volume, while mass percent remains tied to masses.
Scope and private use
Use this calculator when the percentage is explicitly by mass and a defensible final-solution density is available. For medicines, commercial reagents, foods, or regulated samples, read the concentration basis on the label or method before converting. Similar-looking percentage symbols can describe different physical quantities.
The values are calculated in the current browser tab. NexaCurrent does not upload the quantities, formulas, chemical names, element choices, or other information entered here, and no account is needed. Copying is a deliberate action after the answer and working are visible. Refreshing or leaving the page clears the current calculation, so keep a copied result if it is needed for later study.