Molarity Calculator
Calculate the molarity of a solution from the mass of solute, its molar mass and the solution volume, or find the mass needed for a target concentration.
Molarity formulas
Molarity (M) = moles of solute ÷ liters of solution Moles = mass (g) ÷ molar mass (g/mol) Mass = M × volume (L) × molar mass
Worked example
To make 250 mL of 0.5 M sodium chloride (molar mass 58.44 g/mol): moles = 0.5 × 0.250 = 0.125 mol, and mass = 0.125 × 58.44 = 7.305 g. Dissolve it and add water up to a final volume of 250 mL.
Concentration units
| Unit | Meaning |
|---|---|
| M (molar) | mol of solute per liter of solution |
| mM (millimolar) | 0.001 M |
| µM (micromolar) | 0.000001 M |
| m (molal) | mol of solute per kg of solvent |
Find the molar mass by adding the atomic masses of every atom in the formula, from the periodic table.
Frequently asked questions
What is the difference between molarity and molality?
Molarity uses liters of solution; molality uses kilograms of solvent and does not change with temperature.
Do I use the volume of water or of the final solution?
The final solution. Dissolve the solute, then add solvent up to the target volume.
How do I dilute a solution?
Use M1 × V1 = M2 × V2 to find how much stock solution to dilute.
What is 1 M?
One mole of solute in one liter of solution.
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