Molality from Molarity Calculator

About this calculator

Molarity (mol solute per liter of solution) and molality (mol solute per kilogram of solvent) look similar but measure different things — molarity depends on solution volume, which shifts with temperature, while molality depends on solvent mass, which does not, making it the preferred unit for precise work like freezing-point depression or boiling-point elevation.

Converting between them requires the solution's density (ρ, in g/mL) and the solute's molar mass (MW, in g/mol): for one liter of solution, the total mass is 1000·ρ grams, the mass of solute is M·MW grams, and subtracting gives the solvent's mass — so molality m = 1000·M / (1000·ρ − M·MW).

Analytical and physical chemists use this conversion whenever a solution's molarity is known from preparation but a temperature-independent concentration is needed for colligative-property calculations or precise thermodynamic work.