CODDY Tool

Molarity Calculator

Solve for moles, volume or molarity — enter any two, get the third.

Molarity is moles of solute per litre of solution. Enter any two of moles, volume and molarity, and this solves for the third — for making up a solution to a target concentration or working out what concentration you actually ended up with.

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About Molarity Calculator

Molarity — written M, in units of mol/L — is the standard way concentration is expressed in chemistry, precisely because moles are the unit that reaction stoichiometry actually cares about. A recipe that calls for '1 mole of NaOH' needs to become 'this many grams dissolved in this much water,' and molarity is the bridge between those two ways of describing the same amount.

The three quantities — moles, volume, molarity — are related by one equation, M = n/V, which rearranges to whichever one you're solving for. Enter any two and the third follows directly; which two you have depends on what you're actually doing: making up a solution from a known mass usually means you know moles and want the volume for a target molarity, while characterising an unknown solution means you know volume and molarity and want moles.

If you're starting from a mass in grams rather than moles, convert first with the Molar Mass Calculator — moles equals mass divided by molar mass — then bring the result here.

How to use the molarity calculator

  1. Enter two of the three values

    Moles, volume or molarity.

  2. Convert mass to moles first, if needed

    Moles = mass ÷ molar mass.

  3. Read the third value

    Calculated directly from the other two.

Frequently asked questions

What's the difference between molarity and molality?

Molarity is moles of solute per litre of solution (mol/L); molality is moles of solute per kilogram of solvent (mol/kg). They're numerically close for dilute aqueous solutions but genuinely differ, and molality's advantage — being independent of temperature, since mass doesn't change with heat but volume does — is why it's preferred for precise physical chemistry work.

I have a mass in grams, not moles — what do I do?

Convert first: moles = mass in grams ÷ molar mass. The Molar Mass Calculator gives you the second number from a chemical formula, and then moles here.

Does volume mean the volume of solvent, or the final solution?

The final solution's total volume, not the solvent added. This matters because dissolving a solute changes the total volume slightly — 1 mole of solid dissolved into 1 litre of water does not produce exactly 1 litre of solution, which is why a volumetric flask is filled to the mark with solvent after the solute, not measured as a separate solvent volume beforehand.

Why is molarity temperature-dependent?

Because it's defined per litre of solution, and liquids expand slightly as they warm — the same amount of solute ends up in a slightly larger volume at a higher temperature, which technically lowers the molarity. The effect is small enough to ignore for most everyday purposes, but it's the reason precision analytical chemistry sometimes prefers molality instead.

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Molarity Calculator is free to use with no account, no watermark and no usage limits. Last updated 7 September 2026.