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Science — Chemistry

Molarity Calculator

Enter the mass of solute, its molar mass and the solution volume to get the molarity in moles per litre.

Filed by The Statistics Desk  |  Method: M = (mass ÷ molar mass) ÷ litres
e.g. NaCl = 58.44
Molarity
—
Moles of solute per litre of solution.
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Moles of solute—
Volume used—
Mass concentration—
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How the Molarity Calculator Works

Molarity (M) is the concentration of a solution expressed as moles of solute per litre of solution. It is the workhorse unit of the chemistry lab because reactions happen mole-for-mole, not gram-for-gram. To get molarity you first convert the mass of your solute to moles by dividing by its molar mass, then divide by the volume of the finished solution in litres.

Enter the mass you weighed out, the molar mass of the compound (the sum of the atomic weights — sodium chloride is 58.44 g/mol, glucose is 180.16), and the final volume. Volume can be entered in litres or millilitres; millilitres are converted to litres before the division. The tool also reports the mass concentration in grams per litre for convenience.

M = (mass ÷ molar mass) ÷ volumelitres

Frequently Asked Questions

What is the difference between molarity and moles?

Moles count the amount of substance; molarity is moles divided by the volume of solution in litres. Two solutions can hold the same number of moles yet have very different molarities if their volumes differ.

Do I use the volume of solvent or of solution?

Always the total volume of the finished solution, not the volume of solvent you started with. Dissolving a solid changes the volume, which is why solutions are made up to a mark in a volumetric flask.

Where do I find the molar mass?

Add up the atomic masses of every atom in the formula from the periodic table. For example water (H₂O) is 2 × 1.008 + 16.00 = 18.02 g/mol. Many reagent bottles print the molar mass on the label.

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