Molality Calculator
Find the molality of a solution from the amount of solute and the mass of solvent.
Solute input
mol
Solvent mass unit
Moles of solute per kilogram of solvent
- 1
Moles of solute
0.5 - 2
Solvent mass in kg
0.5 - 3
Molality = moles ÷ solvent mass (kg)
0.5 ÷ 0.5 = 1Molality uses mass of solvent only, not total solution mass.
How does this calculator work?
Molality equals moles of solute divided by the mass of the solvent in kilograms (b = n/m). Enter the solute as moles or as a mass with its molar mass, plus the solvent mass in grams or kilograms. The result is given in mol/kg, a temperature-independent measure of concentration.
Formula
How this is calculated
Molality (b) measures concentration as moles of solute divided by the mass of solvent in kilograms: b = n_solute / m_solvent(kg). Choose to enter the solute either directly as moles or as a mass. When you supply a mass, the moles are computed as moles = mass / molar mass, so an accurate molar mass (in g/mol) for the dissolved compound is required.
The solvent mass can be entered in grams or kilograms; grams are converted to kilograms by dividing by 1000 before the division. The result is expressed in mol/kg (also written as "molal" or m). Because molality depends on mass rather than volume, it does not change with temperature, which is its key advantage over molarity (mol/L).
The calculator guards against invalid input: it returns no result if the molar mass or solvent mass is zero or non-numeric. Use the mass of solvent only, not the total mass of the solution, and make sure the molar mass corresponds to the same compound you are weighing.
Frequently asked questions
Molality (mol/kg) divides moles of solute by the mass of the solvent, while molarity (mol/L) divides by the volume of the whole solution. Molality is temperature-independent because mass does not change with temperature.
Use only the mass of the solvent (for example, the water), not the combined mass of solute plus solvent. Molality is defined per kilogram of solvent.
Divide the solute mass by its molar mass (g/mol). For example, 29.25 g of NaCl (molar mass 58.44 g/mol) is 0.5 mol.
Also known as
TG we-Calculate Editorial Team. (2026). Molality Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/molality-calculator
TG we-Calculate Editorial Team. "Molality Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/molality-calculator.
TG we-Calculate Editorial Team, "Molality Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/molality-calculator
@misc{wecalculate_molality_calculator, title = {Molality Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/molality-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?