Molality (symbol m) is the number of moles of solute per kilogram of solvent. It is written as mol/kg or simply m (e.g. 2 m NaCl means 2 moles of NaCl per kg of water).

What is the molality formula?

Molality = moles of solute / mass of solvent in kilograms. Rearranged: moles of solute = molality × kg solvent; kg solvent = moles of solute / molality.

What is the difference between molality and molarity?

Molarity (M) uses volume of solution (L) in the denominator and changes with temperature. Molality (m) uses mass of solvent (kg) and is temperature-independent, making it better for colligative property calculations.

Does molality include the mass of the solute?

No. Molality uses only the mass of the solvent, not the total solution mass. This distinguishes it from molarity, which uses total solution volume.

How do I convert grams of solvent to kilograms?

Divide by 1000. For example, 500 g of water = 0.5 kg. This calculator accepts grams and converts automatically when you select the g unit.

What are typical molality values?

Dilute aqueous solutions are often 0.01–1 mol/kg. Concentrated solutions can reach 5–20 mol/kg depending on the solubility of the solute.

Molality Calculator

Calculate molality from moles of solute and mass of solvent, or solve for moles or solvent mass given the other two values.

Solve For

Moles of Solute (mol)

Solvent Mass

Mass of solvent only — do not include solute mass.

Formula Reference

m = n / kg_solvent

m = molality (mol/kg)
n = moles of solute (mol)
kg_solvent = mass of solvent (kg)

Result

Live

Enter values on the left to calculate.

All three values will be shown once computed.

Molality

—

mol/kg

Variable	Symbol	Value	Unit
Molality	m	—	mol/kg
Moles of Solute	n	—	mol
Solvent Mass	kg_solvent	—	kg
Also in grams		—	g

Working

Summary

Molality (m) is a concentration unit defined as the number of moles of solute dissolved per kilogram of solvent. Unlike molarity, molality does not change with temperature because it is based on mass rather than volume, making it the preferred unit for colligative property calculations such as boiling-point elevation and freezing-point depression. This calculator solves the three-variable molality equation — enter any two known values and the tool computes the third instantly.

How it works

Select which variable you want to solve for: Molality, Moles of Solute, or Solvent Mass.
Enter the two known values in the appropriate fields.
The calculator applies the formula m = n / kg_solvent and displays the result.
Switch the solvent mass unit between kilograms and grams as needed.
Results update live — no button press required.

Use cases

Chemistry students solving colligative property problems (boiling-point elevation, freezing-point depression).
Lab technicians preparing solutions where temperature stability of concentration is required.
Calculating how many moles of solute are needed to reach a target molality.
Finding how much solvent is required to dissolve a known amount of solute at a given molality.
Electrochemistry work requiring concentration expressed independently of temperature.
Cross-checking textbook exercises on solution stoichiometry.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu