Molarity Calculator
Calculate the molarity of a solution from solute mass, molar mass, and volume.
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1 mol/L
About this calculator
How This Molarity Calculator Works
Enter the mass of solute, its molar mass, and the total solution volume, and the calculator returns the molarity — the standard measure of solution concentration in chemistry.
Worked Example
Dissolving 58.44 g of table salt (NaCl, molar mass 58.44 g/mol) in 1 L of solution produces exactly a 1 mol/L (1 M) solution.
The Formula
Molarity = Moles of solute ÷ Liters of solution, where moles of solute is found first as Mass ÷ Molar mass. Molar mass is the mass of one mole of a substance in grams, found by summing the atomic masses of every atom in its chemical formula.
A Key Detail: Solution Volume, Not Solvent Volume
Molarity is defined using the total volume of the final solution — after the solute is dissolved — not the volume of solvent (like water) used before mixing. Since dissolving a solute can slightly change the total volume, precise lab work typically dissolves the solute and then adds solvent up to a calibrated final volume mark, rather than simply adding a fixed amount of solvent.
Molarity vs. Molality
Molarity (mol/L) is defined relative to solution volume, which can expand or contract slightly with temperature. Molality (mol/kg) is defined relative to the solvent's mass instead, which doesn't change with temperature — making molality the preferred unit in contexts where temperature varies, like some physical chemistry calculations, while molarity remains the standard for everyday lab and classroom use.
Worked example
Dissolving 58.44 g of table salt (NaCl, molar mass 58.44 g/mol) in 1 L of solution produces exactly a 1 mol/L (1 M) solution.
Frequently asked questions
What is molar mass, and where do I find it?
Molar mass is the mass of one mole of a substance, in grams per mole — it's calculated by summing the atomic masses of every atom in the compound's chemical formula, and can be found on a periodic table or a compound's reference data.
What's the difference between molarity and molality?
Molarity (mol/L) is moles of solute per liter of solution; molality (mol/kg) is moles of solute per kilogram of solvent. Molarity is more common in general chemistry, while molality is preferred when temperature changes are involved, since it doesn't depend on solution volume, which can expand or contract with temperature.