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Molarity Calculator

Find the molarity of a solution.

Result

0.250 mol/L

How it is calculated

Molarity is the concentration of a solution: M = n ÷ V, where n is the amount of dissolved substance (solute) in moles and V is the volume of the whole solution in litres. The answer is in mol/L, written as M, shown with three decimals. Volume must be above zero. If you only know the mass of solute, first divide by the molar mass (g/mol) to obtain moles. Molarity depends on temperature slightly, because the volume of a liquid changes as it warms; the formula itself ignores that.

Worked example

You dissolve 0.5 mol of a salt and make the solution up to 2 litres. Molarity = 0.5 ÷ 2 = 0.25. The tool shows 0.250 mol/L. If you took 100 mL (0.1 L) of it, that portion would hold 0.025 mol, because concentration stays the same however much you pour out.

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Common mistakes

  • Using the volume of solvent instead of the final solution. The litres should be the total volume after dissolving.
  • Entering millilitres. 250 mL must be typed as 0.25 L, otherwise the molarity is 1,000 times too small.
  • Entering grams where moles are expected. Divide the mass by the molar mass first.
  • Confusing molarity with molality. Molality is moles per kilogram of solvent, which is a different number.
  • Forgetting dilution. Adding water to a solution lowers the molarity, because the same moles are spread over a larger volume.

About this calculator

This calculator finds molarity, M = moles of solute ÷ liters of solution, the standard unit chemists use to express how concentrated a solution is.

Chemistry students use it constantly in lab reports and titration calculations, and lab technicians use it to prepare reagents at an exact concentration — get the molarity wrong and an experiment's results become meaningless. Enter any two of moles, volume, or mass with molar weight and it fills in the rest.

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