Calculate molality from solute mass, molar mass and solvent mass, with moles and mass percent.
Result
How to use this tool
Enter the solute mass in grams and its molar mass in g/mol.
Enter the solvent mass in grams or kilograms.
Read moles, solvent mass in kg, molality and mass percent.
Remember this is per kg of solvent, not per litre of solution.
Formula & worked example
58.44 g of NaCl (molar mass 58.44 g/mol) in 1000 g of water is 1 mol/kg.
Limitations — read this before you rely on it
Assumes the solute dissolves fully without reacting with the solvent. For electrolytes, the effective particle molality is molality × van’t Hoff factor.
Frequently asked questions
Molality is moles of solute per kilogram of solvent, written mol/kg (molal, m).
Molarity is per litre of solution and changes with temperature as volume changes; molality is per kilogram of solvent and does not.
Only the solvent, not the whole solution. For a salt-water mix, enter the water mass.
Yes: moles = mass ÷ molar mass, and molality needs moles, so the molar mass is essential.
Yes: ΔT = K × molality × van’t Hoff factor is a standard colligative-property use.