How do I calculate molarity?

Divide the moles of solute by the volume of solution in liters. The result is in mol/L, written M.

Is it liters of solvent or of solution?

Of the final solution. Dissolving solute adds volume, so measuring the solvent first gives a slightly wrong concentration.

What is the difference between molarity and molality?

Molarity is per liter of solution and shifts with temperature as volume expands. Molality is per kilogram of solvent and does not.

Molarity Calculator

How molarity works

Molarity expresses concentration as the number of moles of dissolved substance per liter of solution, written M = moles ÷ liters. It is the most common way chemists describe how strong a solution is.

Choose which of the three quantities you want, and the calculator rearranges the same relationship to solve for it: molarity from moles and volume, moles from molarity and volume, or volume from moles and molarity.

Using the result

Molarity tells you how much solute sits in each liter, which lets you scale a recipe up or down or work out how much to weigh out for a target concentration.

Solve for moles to find how much solute a given volume contains.
Solve for volume to find how much solution a fixed amount of solute makes.

Practical tips

Molarity is based on the volume of the finished solution, not the volume of solvent you started with, because dissolving a solid can change the total volume.

Convert millilitres to liters before entering volume.
Convert a mass of solute to moles using its molar mass first.

Caveats and common mistakes

Volume must be greater than zero when solving for molarity, and molarity must be positive when solving for volume, since both involve dividing by that value. Molarity also shifts slightly with temperature because liquid volume expands and contracts.

Formula

M = moles / liters

Frequently asked questions

How do I calculate molarity?: Divide the moles of solute by the volume of solution in liters. The result is in mol/L, written M.
Is it liters of solvent or of solution?: Of the final solution. Dissolving solute adds volume, so measuring the solvent first gives a slightly wrong concentration.
What is the difference between molarity and molality?: Molarity is per liter of solution and shifts with temperature as volume expands. Molality is per kilogram of solvent and does not.