Molarity calculator
Calculate the molarity of a solution from solute mass, molar mass and volume.
Molarity (M) is the concentration in moles of solute per liter of solution.
How the calculation works
Molarity (M) measures a solution's concentration: how many moles of solute per liter of solution. It's a two-step calculation.
1. Amount of substance: n = mass (g) ÷ molar mass (g/mol)
2. Molarity: M = n ÷ volume (L)
Step-by-step example
58.5 g of salt (NaCl, molar mass 58.5 g/mol) in 1 liter of water:
- Moles: 1 mol
- Molarity: 1 mol/L (1 M)
Examples
- 40 g of NaOH (40 g/mol) in 0.5 L: 1 mol ÷ 0.5 = 2 mol/L.
- Doubling the volume (same mass) halves the molarity.
Frequently asked questions
Where do I find the molar mass?
Add the atomic masses of the formula's elements (periodic table). E.g. NaCl ≈ 58.5 g/mol.
Volume of solution or of water?
Of the final solution (solute + solvent), not just water. That is why you fill to the flask's mark.
Molarity vs molality?
Molarity is mol per liter of solution; molality is mol per kg of solvent. Molarity varies with temperature; molality does not.
Is the volume that of the water or the final solution?
The final solution. The solute occupies volume too, which is why a volumetric flask is filled to the mark after dissolving.
Molarity versus molality?
Molarity divides moles by solution volume (mol/L); molality divides by solvent mass (mol/kg). Molality is temperature-independent.
Does molarity change with temperature?
Yes, slightly. The solution expands with heat, so the same solute occupies more volume and mol/L drops.
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See all →Updated on June 18, 2026 · by Rafael Rossi · Methodology & sources