Molarity Calculator
Molarity is the amount of dissolved substance per litre of solution.
Enter Values
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How to use this calculator
- Enter the molar mass of the solute in g/mol (look it up from the periodic table or a molar-mass calculator).
- Enter the mass of solute you dissolved, in grams, and the total volume of the finished solution in litres.
- Read off the molarity in mol/L (M) and the moles of solute; use the steps panel to see the working.
How it works
Molarity is the amount of dissolved substance per litre of solution. It is calculated as M = n ÷ V, where n is the number of moles of solute and V is the total solution volume in litres. The unit is mol/L, also written M (molar).
The moles of solute come from n = mass ÷ molar mass. Combining the two gives M = mass ÷ (molar mass × volume). Because molarity is defined per litre of solution, always use the total volume of the final mixture — not the volume of pure solvent you started with.
Worked example
0.4 M sodium chloride solution. To find the molarity of 11.688 g of table salt (NaCl, molar mass 58.44 g/mol) dissolved in 0.5 L of solution: first find the moles, n = 11.688 ÷ 58.44 = 0.2 mol. Then molarity M = 0.2 mol ÷ 0.5 L = 0.4 mol/L. The solution is 0.4 molar (0.4 M).
Common mistakes
- Using the volume of solvent added instead of the total volume of the finished solution — molarity is per litre of solution.
- Entering the volume in millilitres instead of litres; 500 mL must be entered as 0.5 L.
- Confusing molarity (mol per litre of solution) with molality (mol per kilogram of solvent) — this tool computes molarity.
Frequently asked questions
What is the formula for molarity?
Molarity M = moles of solute ÷ litres of solution, or M = mass ÷ (molar mass × volume in litres). The result is in mol/L, also written as M (molar).
How do I find the molar mass to enter?
Add up the atomic masses of every atom in the compound's formula. For example, NaCl is 22.99 (Na) + 35.45 (Cl) = 58.44 g/mol. A periodic table or molar-mass calculator gives these values.
Is molarity the same as molality?
No. Molarity is moles of solute per litre of solution and depends on temperature (volume expands with heat). Molality is moles of solute per kilogram of solvent and is temperature-independent. This calculator computes molarity.
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