Molarity Calculator — molar concentration (M = mol/L)

How it works

Molarity (M) is the most common way to express the concentration of a solution. It is defined as the number of moles of solute dissolved per litre of solution (OpenStax Chemistry):

M = moles of solute ÷ litres of solution

The key details are the units: the amount of solute must be in moles (convert from grams using the molar mass if needed) and the volume must be the total solution volume in litres — not the volume of solvent you started with, and not millilitres. A 1-molar (1 M) solution contains one mole of solute in every litre.

Molarity is central to chemistry because reactions happen between amounts (moles) of substances, and measuring a volume of a solution of known molarity is a convenient way to dispense a precise number of moles. Rearranging the definition lets you find any of the three quantities: moles = M × litres, and litres = moles ÷ M.

Worked example

Dissolving 0.133 mol of sucrose in 355 mL (0.355 L) of soft drink:

M = 0.133 ÷ 0.355 ≈ 0.375 M

If you only had 0.5 L of that same 0.375 M solution, it would contain 0.375 × 0.5 = 0.188 mol of sucrose.

Frequently asked questions

How do you calculate molarity?

Divide the moles of solute by the volume of solution in litres. For 0.5 mol in 1 L, the molarity is 0.5 mol/L, written 0.5 M.

What is the difference between molarity and moles?

Moles measure an amount of substance; molarity measures a concentration — moles per litre. The same number of moles gives a higher molarity in a smaller volume.

Do I use the volume of solvent or solution?

The total volume of the final solution, not the solvent alone. Dissolving solute can change the volume slightly, so molarity is defined against the solution's measured volume.

How do I convert grams to moles for this?

Divide the mass in grams by the substance's molar mass (g/mol) to get moles, then divide by the volume in litres. A dedicated moles calculator can do the first step.

What does a 1 M solution mean?

A 1-molar solution contains exactly one mole of solute per litre of solution. Two litres of it would contain two moles; half a litre would contain half a mole.

How is molarity different from molality?

Molarity is moles of solute per litre of *solution*; molality is moles per kilogram of *solvent*. Molarity is easier to measure by volume but changes slightly with temperature, while molality does not.