Molarity calculator: mass, volume and concentration
Work out the molarity (mol/L) of a solution from the mass dissolved, the molar mass and the volume, or solve for any one of them, such as how many grams you need for a solution.
c = m ÷ (M × V)
c is the molarity in mol/L, m the mass of solute in grams, M its molar mass in g/mol and V the volume of solution in liters.
How to use the calculator
Pick the value you want under Solve for, then fill in the other three. To make a solution, solve for the mass: enter the molarity you want, the molar mass and the volume. You can look up a molar mass with the molar mass calculator.
Use liters for the volume: 250 mL is 0.25 L.
Worked example: 0.2 M sodium chloride
To make 500 mL of 0.200 mol/L sodium chloride, multiply molarity by volume to get moles, 0.200 × 0.500 = 0.100 mol, then multiply by the molar mass of NaCl, 58.44 g/mol: 0.100 × 58.44 = 5.844 g. Dissolve that in water and make it up to 500 mL in total.
Molarity and moles
Molarity is moles of solute per liter of solution, so n = c × V. Moles come from mass by n = m ÷ M. Putting the two together gives c = m ÷ (M × V), the formula this calculator uses.
Molarity uses the volume of the whole solution, not of the water you add. That is why solutions are made up to the mark in a volumetric flask.
FAQ
What is molarity?
Molarity is the concentration of a solution in moles of solute per liter of solution, written mol/L or M. A 1 M solution of glucose contains 1 mole, 180.16 g, of glucose in every liter.
How do I convert mL to L?
Divide by 1,000: 250 mL is 0.250 L and 50 mL is 0.050 L.
What is the difference between molarity and molality?
Molarity is moles per liter of solution, while molality is moles per kilogram of solvent. Molality does not change with temperature, because it uses masses instead of a volume.