Molarity CalculatorFree online science calculator — instant results, no sign-up
Calculate solution molarity from moles of solute and volume.
About the Molarity Calculator
The Molarity Calculator calculates a solution’s molar concentration from the moles of solute and the total solution volume in liters. With the default inputs of 0.5 mol and 0.25 L, it returns a molarity of 2 mol/L.
- Solute (mol)
- The amount of dissolved solute, measured in moles (mol), with a default of 0.5 mol.
- Solution volume (L)
- The final total volume of the solution, measured in liters (L), with a default of 0.25 L.
Formula and method
M = n ÷ V = 0.5 mol ÷ 0.25 L = 2 mol/L
- MMolarity of the solution, expressed in moles per liter (mol/L).
- nAmount of solute in moles (mol).
- VFinal solution volume in liters (L).
Divide the amount of solute in moles by the final solution volume in liters. Using the defaults, divide 0.5 by 0.25 to obtain 2 mol/L. The solute amount must be nonnegative, and the solution volume must be greater than zero.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Solute0.5 mol
- Solution volume0.25 L
Results
- Molarity2 mol/L
- FormulaM = moles ÷ liters
How to use the Molarity Calculator
- 1Enter the amount of solute in Solute (mol); leave it at 0.5 to follow the worked example.
- 2Enter the final solution volume in Solution volume (L); leave it at 0.25 for the worked example.
- 3Confirm that the amount is in moles and the volume is in liters, converting other units before entry.
- 4Calculate the result by dividing the moles of solute by the liters of solution.
- 5Read the Molarity result of 2 mol/L and check the Formula row, M = moles ÷ liters.
Reading your result
The Molarity row reports solute concentration in mol/L. The default result, 2 mol/L, means the solution contains 2 moles of solute per liter of solution; the actual 0.25 L sample contains 0.5 mol. The Formula row shows M = moles ÷ liters, identifying the division used to obtain the result.
Limitations
Use the final solution volume, not the volume of solvent before adding solute. The calculation assumes the entered solute amount is dissolved and uniformly distributed. It does not check solubility, account for chemical reactions or dissociation, or convert solute mass into moles. Zero or negative volume is invalid, and negative solute amounts are not physically meaningful. Molarity can change with temperature because solution volume can change; accuracy also depends on the precision of the inputs.
Common questions
Why do 0.5 mol and 0.25 L give 2 mol/L?+
Molarity is moles divided by liters: 0.5 ÷ 0.25 = 2. The result describes concentration, not the total number of moles in the sample.
Should I enter solvent volume or final solution volume?+
Enter the final solution volume after the solute has dissolved. Adding solute can change the volume, so solvent volume alone may give an incorrect molarity.
Can I enter grams of solute instead of moles?+
No. First divide the solute mass in grams by its molar mass in g/mol, then enter the resulting amount in Solute (mol).
Does this calculator give the concentration of every ion in a dissolved salt?+
No. It calculates molarity from the solute amount you enter. Individual ion concentrations require additional information about dissociation, stoichiometry, and any relevant chemical equilibria.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
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Results are estimates for informational purposes and are not financial, medical or legal advice.