Molarity Calculator guide
Molarity Calculator: Concentration, Mass and Dilutions
Use our molarity calculator to work out the mass of solute you need, the molarity of a solution or a C₁V₁ = C₂V₂ dilution, with worked examples.
By the AllCalculator editorial teamUpdated 15 October 20261 min read
Making up solutions accurately is a basic lab skill, and the maths is simple once you know the formula. Our Molarity Calculator handles the common calculations and dilutions.
How to use the calculator (Molarity Calculator)
- Choose what you want to find: the mass needed, the molarity, the volume, or a dilution.
- Enter the molar mass of the solute. 58.44g/mol is sodium chloride.
- Enter the other values.
The key formulas
- Moles = mass ÷ molar mass
- Molarity (mol/L) = moles ÷ volume in litres
- So mass = molarity × volume (L) × molar mass
- Dilution: C₁V₁ = C₂V₂
A worked example
With the calculator's default settings, making 250mL of 0.5mol/L sodium chloride:
- Moles: 0.5 × 0.25 = 0.125mol
- Mass: 0.125 × 58.44 = 7.305g
Dissolve 7.305g of NaCl in some water, then make up to 250mL in a volumetric flask.
Dilutions
To make 100mL of 0.5mol/L from a 2mol/L stock:
- V₁ = C₂V₂ ÷ C₁ = 0.5 × 100 ÷ 2 = 25mL of stock
- Make up to 100mL with 75mL of water
For unit conversions, see our Unit Converter, and for measurement uncertainty our Error Propagation Calculator.
Frequently asked questions
What's the difference between molarity and molality?
Molarity is moles per litre of solution. Molality is moles per kilogram of solvent, and doesn't change with temperature.
How do I find the molar mass?
Add up the relative atomic masses of every atom in the formula. For NaCl: 22.99 + 35.45 = 58.44g/mol.
Why make up to the final volume?
Adding a solute changes the volume a little, so you dissolve it first and then add solvent up to the mark.
Use the Molarity Calculator to check your calculations before you weigh anything out.
Sources and further reading
Links open official and independent websites in a new tab.
This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.