Molarity Calculator
Pick one of four modes. Molarity divides the moles of solute by the volume of the solution in liters. Tick the box to enter the mass in grams and the molar mass instead of moles. Moles divides a mass in grams by the molar mass. Molarity to Grams gives the mass of solute to weigh for a target molarity and volume, in liters or milliliters. Dilution solves C₁V₁ = C₂V₂ for the value you leave out, with concentrations in mol/L and volumes in liters. Results are rounded to 6 decimal places.
How to use the Molarity Calculator
- Enter your numbers in the Molarity Calculator above.
- Press the Calculate button to see the result.
- To try other numbers, change any value and press the button again.
The molarity formulas
M = n / V · · · n = m / MW · · · m = M × V × MW · · · C₁V₁ = C₂V₂
M is the molarity in mol/L, n the moles of solute and V the volume of the whole solution in liters. m is the solute mass in grams and MW its molar mass in g/mol. Dilution adds solvent and keeps the moles of solute, so the concentration times the volume is the same before and after.
Worked example
Dissolve 5.85 g of NaCl, molar mass 58.44 g/mol, and make the solution up to 250 mL. Tick the mass box and enter 5.85, 58.44 and a volume of 0.25 L. The calculator shows 0.100103 mol and a molarity of 0.400411 M. To dilute 0.05 L of a 6 M solution to 1 M, solve for V₂: 6 × 0.05 / 1 = 0.3 L. To make 500 mL of 0.4 M NaCl, use Molarity to Grams: 0.4 × 0.5 = 0.2 mol, and 0.2 × 58.44 = 11.688 g.
Frequently asked questions
What's the difference between molarity, molality and normality?
Molarity (M) is moles of solute per liter of solution. Molality (m) is moles of solute per kilogram of solvent. Normality (N) counts equivalents per liter and depends on the reaction. This calculator works in molarity only.
How do I convert molarity to grams?
Multiply the molarity by the volume in liters and by the molar mass, or use Molarity to Grams mode. For 0.5 L of 0.4 M NaCl that is 0.4 × 0.5 × 58.44 = 11.688 g. Molarity mode with 11.688 g, 58.44 g/mol and 0.5 L gives 0.4 M back as a check. Dissolve the solute first and then make the solution up to the full volume, because the volume is that of the solution, not of the water you add.
Which molar mass should I use?
The molar mass of the exact form you weigh out. A hydrate includes its water, so its molar mass is higher than that of the dry salt and the mass to weigh goes up with it. The molecular weight calculator works out a molar mass from a chemical formula.
Does temperature affect molarity?
Yes. Molarity is per liter of solution, and a solution's volume changes with temperature, so its molarity changes too. The calculator uses the volume you enter.