Molarity calculator
Molarity from mass and volume, the mass to weigh for a solution, or a dilution.
About this calculator
This molarity calculator works out the molar concentration of a solution from the mass dissolved, the molar mass and the volume.
It also tells you how much solute to weigh for a solution you want to make, and how to dilute a stock solution with C₁V₁ = C₂V₂.
How it works
Molarity is moles of solute ÷ litres of solution. Moles = mass ÷ molar mass, so M = mass ÷ (molar mass × volume). In a dilution the amount of solute stays the same, so C₁V₁ = C₂V₂.
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Worked example
- Work out: Molarity of a solution
- Molar mass: 58.44 g/mol
- Mass dissolved: 5.844 g
- Volume of solution: 100 mL
Molarity: 1 mol/L
Common questions
What does 1 M mean?
One mole of solute per litre of solution. For table salt, 58.44 g made up to 1 litre gives 1 M.
What is the difference between molarity and molality?
Molarity is per litre of solution; molality is per kilogram of solvent. Molality doesn't change with temperature.
How do I dilute a solution?
Use C₁V₁ = C₂V₂. To make 500 mL of 0.1 M from a 2 M stock, take 25 mL of stock and add water up to 500 mL.
Sources and further reading
The story behind it
Where the idea came from: Since 2019, the mole has been defined by a fixed number of particles: exactly 6.02214076 × 10²³.
That number, the Avogadro constant, links the mass you weigh on a balance to the number of molecules. A 1 M solution holds that many molecules of solute in every litre.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, so please double-check anything important.
- Spotted a mistake? Tell us and we'll look into it.
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