Molality Calculator
Calculate molality from moles of solute and mass of solvent, and compare with molarity.
About Molality Calculator
Molality uses solvent mass rather than solution volume, so it is independent of temperature. That is why colligative property equations — boiling point elevation, freezing point depression — are written in molality. For dilute aqueous solutions molality and molarity are nearly equal, but they diverge markedly at high concentration or in dense solvents.
Formula
Molality
b = moles of solute ÷ kilograms of solvent
- molality
- Based on solvent mass, so it does not change with temperature
- molarity
- Based on solution volume, which expands when heated
Worked example
With the default values below, Molality Calculator returns Molality of 0.50000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Moles of soluteminimum 0 mol
- 0.5 mol
- Mass of solventminimum 0 kg
- 1 kg
- Solution densityminimum 0 kg/L
- 1.02 kg/L
- Molar mass of the soluteminimum 0 g/mol
- 58.44 g/mol
Results
- Molality
- 0.50000 mol/kg
- Mass of Solute
- 29.2200 g
- Total Solution Mass
- 1.02922 kg
- Approximate Molarity
- 0.49552 mol/L
- Mass Percent of Solute
- 2.8390%
Step by step
- 1Values used
- 2Molality
- 3Molality= 0.50000 mol/kg
- 4Mass of Solute= 29.2200 g
- 5Total Solution Mass= 1.02922 kg
- 6Approximate Molarity= 0.49552 mol/L
- 7Mass Percent of Solute= 2.8390
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Molality calculated?
b = moles of solute ÷ kilograms of solvent Molality uses solvent mass rather than solution volume, so it is independent of temperature. That is why colligative property equations — boiling point elevation, freezing point depression — are written in molality.
Why does Molality matter?
For dilute aqueous solutions molality and molarity are nearly equal, but they diverge markedly at high concentration or in dense solvents.
What values do I need to enter?
This calculator takes 4 inputs: Moles of solute, Mass of solvent, Solution density, Molar mass of the solute. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.