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Molarity Calculator

Choose what to find. Enter the mass, the molar mass and the volume to get the molarity, or the dilution values to find the final volume and the solvent to add.

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How we calculate it

Molarity is the number of moles of solute per liter of solution, M = n ÷ V. The number of moles is the mass divided by the molar mass, n = m ÷ MM. So 58.44 g of table salt (molar mass 58.44 g/mol) in 1 liter of solution is 1 mol ÷ 1 L = 1 mol/L. To prepare a solution, mass = M × V × MM, and to find a volume, V = n ÷ M.

For a dilution, the amount of solute stays the same, so M1 × V1 = M2 × V2. Diluting 25 mL of a 6 mol/L solution to 0.5 mol/L gives a final volume of 6 × 25 ÷ 0.5 = 300 mL, which means adding 275 mL of solvent (choose mL as the volume unit).

Assumptions and limits

  • The volume is the volume of the finished solution, not of the solvent you start with. Dissolving a solid usually changes the volume a little.
  • Find the molar mass of your compound with the molecular weight calculator.
  • A solution can only be made weaker by dilution. The final molarity must not be higher than the starting molarity.

Frequently asked questions

How do I calculate molarity?

Divide the moles of solute by the liters of solution. The moles are the mass in grams divided by the molar mass in g/mol. 5.844 g of NaCl in 100 mL is 0.1 mol ÷ 0.1 L = 1 mol/L.

How many grams do I need for a 0.5 M solution?

Multiply the molarity, the volume in liters and the molar mass. For 250 mL of 0.5 M NaCl that is 0.5 × 0.25 × 58.44 = 7.305 g.

What is M1V1 = M2V2?

It is the dilution equation. The moles of solute before and after adding solvent are the same, so concentration times volume is the same on both sides.

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Worked example (a fixed example using the starting numbers, it does not change as you type)

Inputs: Find the = Molarity (from mass and volume); Mass of solute = 58.44; Mass unit = Grams (g); Molar mass of the solute (g/mol) = 58.44; Volume of solution = 1; Volume unit = Liters (L).

  • Molarity 1 mol/L
  • Moles of solute 1 mol
  • Concentration 58.44 g/L

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Last reviewed: . Formulas and assumptions are described on our methodology page. For information only; not professional advice.