Molality Calculator

About this calculator

Molality measures solution concentration as m = moles of solute / kilograms of solvent (units mol/kg, sometimes called "molal"). Because it's defined by mass of solvent rather than volume of solution, molality doesn't shift with temperature the way molarity does (volume expands or contracts as liquids heat and cool), making it the preferred unit whenever precise, temperature-independent concentration matters.

Physical chemists rely on molality for colligative-property calculations — freezing-point depression (ΔTf = Kf·m·i) and boiling-point elevation (ΔTb = Kb·m·i) — where the constants Kf and Kb are only valid when concentration is expressed this way. Lab chemists preparing standard solutions for cryoscopy or ebullioscopy experiments, and students working through physical chemistry problem sets, use molality for exactly this reason.