Four calculators, one panel.
Pick a mode below — mix and match units freely, everything recalculates live as you type, and every result explains itself.
How much solute you're dissolving.
Grams per mole of the solute (e.g. NaCl ≈ 58.44 g/mol).
Use this if you already know the moles, without needing a molar mass.
The mass of the pure solvent — usually water, before mixing.
The known molal concentration.
Must be greater than zero to solve for moles.
Leave blank to see moles only, or fill it in to also see the solute mass.
Must be greater than zero to solve for solvent mass.
The known amount of solute in moles.
Any molal concentration converts the same way, regardless of the solute.
Two inputs to an answer.
No manual required — but here's the entire flow in four moves.
Pick a mode
Molality for solute + solvent → mol/kg. Solve moles or Solve solvent mass for the two reverse cases. Unit converter for switching between molal units on their own.
Enter what you know
Type a number and pick its unit from the dropdown right next to it — enter solute as mass plus molar mass, or as moles directly, whichever you have. The example chips fill everything in with one tap.
Read the results
The main answer sits up top in large type. Related values in other units sit below, and the exact formula with your numbers substituted sits at the bottom.
Trust the checks
Impossible inputs — negative mass, a zero solvent mass or molality you're trying to divide by — get flagged with a plain-English reason instead of a wrong or broken answer. Copy any result set with one click.
One formula, three ways to use it.
Every mode above is the same equation, just solved for a different letter.
Molality
Moles of solute (n) divided by the mass of solvent in kilograms. If you only have a mass, first find n = mass ÷ molar mass.
Solving for moles
Multiply the known molality by the mass of solvent in kilograms.
Solving for solvent mass
Divide the moles of solute by the known molality.
Questions people actually ask.
The short answers — with the long ones one tap away.
What is molality?+
Molality is a measure of concentration equal to the moles of solute dissolved per kilogram of solvent, written mol/kg and sometimes shown with the symbol m. Unlike molarity, it doesn't change with temperature, since it's based on mass rather than volume.
What is the formula for molality?+
Molality is m = n ÷ kg, where n is the moles of solute and kg is the solvent's mass in kilograms. If you only know the solute's mass, first find moles with n = mass ÷ molar mass, then divide by the solvent's mass.
What's the difference between molality and molarity?+
Molality divides moles of solute by the mass of the solvent in kilograms, while molarity divides moles of solute by the volume of the whole solution in litres. Because molality is mass-based, it stays constant as temperature changes, while molarity can shift slightly as the solution expands or contracts.
How do I find the moles of solute from its mass?+
Divide the solute's mass in grams by its molar mass in grams per mole: n = mass ÷ molar mass. Enter the mass, its unit and the molar mass in the Molality tab and the calculator handles the conversion automatically.
How do I find the mass of solvent for a target molality?+
Rearrange the formula: kg = n ÷ m. Enter the known molality and the moles (or mass plus molar mass) of solute in the Solve solvent mass tab and the calculator returns the required solvent mass in kilograms, grams, pounds and ounces.
What units is molality measured in?+
The standard unit is moles per kilogram (mol/kg). Related units include millimoles per kilogram, micromoles per kilogram, moles per gram and millimoles per gram. The Unit converter tab switches between all of them instantly.
Is this tool free, and where does my data go?+
It's completely free and runs entirely in your browser — nothing you type is uploaded, logged, or sent to any server. No account, no sign-up, no limits.