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Molarity Calculator
Your solution
Molar mass: 58.44 g/mol
Enter the volume in litres: 500 mL is 0.50 L. The field for the value you are solving for is filled in by the calculator.
Example: 58.44 g of sodium chloride (NaCl) in 1.00 L of solution → 1.00 M.
Behind the numbers
How molarity is calculated
Molarity is moles of solute divided by litres of solution. If you start with a mass, first turn it into moles by dividing by the compound's molar mass. The same equation rearranges to find moles (molarity × volume), volume (moles ÷ molarity) or mass (moles × molar mass).
Worked example — 58.44 g of NaCl in 1.00 L: first the moles, n = 58.44 g ÷ 58.44 g/mol = 1.00 mol. Then the molarity, M = 1.00 mol ÷ 1.00 L = 1.00 M. A custom compound works the same way: 50 g of a compound with a molar mass of 100 g/mol is 0.50 mol, so in 2.00 L it is 0.25 M.
Examples
Example solutions
| Solution | Solve for | Answer |
|---|---|---|
| 58.44 g NaCl in 1.00 L | Molarity | 1.00 M |
| 0.50 mol in 2.00 L | Molarity | 0.25 M |
| 2.00 M, 0.50 L | Moles | 1.00 mol |
| 1.00 mol, 0.50 M | Volume | 2.00 L |
| 0.25 mol glucose (180.16 g/mol) | Mass | 45.04 g |
| 50 g “Test Salt” (100 g/mol) in 2.00 L | Molarity | 0.25 M |
Tips before you use it
Always use litres for volume. Divide milliliters by 1,000 first — 250 mL is 0.25 L, not 250 L.
Molarity is about the final solution volume, not the water added. Dissolve the solute, then top the solution up to the target volume.
To dilute a solution, use M1V1 = M2V2: the moles before dilution equal the moles after.
Double-check the molar mass for hydrates — for example, copper sulfate pentahydrate (CuSO4·5H2O) includes the water in its molar mass.
Good to know
Frequently asked questions
What is molarity?
Molarity is the concentration of a solution: the number of moles of solute in each litre of solution, written in mol/L or M. A 1.00 M solution has 1.00 mole of solute in every litre.
How is molarity different from moles?
Moles count how much solute you have; molarity is how concentrated it is. The same 1.00 mole makes a 1.00 M solution in 1 litre, but only a 0.50 M solution in 2 litres.
How do I find the molar mass of a compound?
Add up the atomic masses of all the atoms in its formula. For sodium chloride, NaCl, that is about 22.99 for sodium plus 35.45 for chlorine, about 58.44 g/mol. Pick a compound in the list above and its molar mass fills in automatically.
Can I enter the volume in milliliters?
Yes, but convert it first: divide milliliters by 1,000 to get litres. A volume of 500 mL is 0.50 L, and 250 mL is 0.25 L.