Molarity Calculator
Enter the moles of solute and the volume of solution and get the molarity in mol/L — the single number that tells you how concentrated a solution is.
Moles and volume in, molarity out
Enter the amount of solute in moles and the volume of solution in litres and the calculator returns the molarity (moles ÷ volume) in mol/L.
Use the total volume
Use the total volume of the finished solution in litres — solute plus solvent — not the volume of solvent you started with.
What is a molarity calculator?
Moles over litres, one clear number
A molarity calculator turns two measurements — how much substance is dissolved (its amount in moles) and how much solution there is (its volume in litres) — into a single number: the molarity, or molar concentration, of the solution. Molarity is what separates a faint pinch of salt in a bucket from a saturated brine, and it is the everyday language of the chemistry lab. That makes it the go-to figure for preparing solutions to a target strength, running titrations, and scaling a recipe up or down while keeping the concentration the same.
Enter the moles of solute and the volume of solution in litres to get the molarity in mol/L instantly.
One short formula: divide the moles of solute by the volume of solution.
M = moles ÷ volumeThe capital letter M is the standard symbol for molar concentration, and mol/L is often written simply as M and read as "molar". Because molarity is moles divided by litres, the units follow automatically: moles ÷ litres gives moles per litre (mol/L). A solution labelled 0.25 M therefore holds a quarter of a mole of solute in every litre.
Suppose you dissolve 0.5 mole of solute and make the solution up to 2 litres.
Confirm the volume
Use the total volume of the finished solution — 2 litres — not the solvent you started with.
Divide moles by volume
0.5 ÷ 2 = 0.25 — the moles of solute spread across that volume.
Read the molarity
0.25 mol/L — a quarter-molar (0.25 M) solution.
The single molarity figure tells a surprisingly rich story. First, it measures how concentrated the solution is: a higher number means more solute packed into each litre, so 2 mol/L is eight times as concentrated as 0.25 mol/L. The benchmark is 1 M — one mole per litre — with anything well below that counting as dilute and anything well above as concentrated; for reference, household vinegar is roughly 0.8 M acetic acid. It is crucial to remember that molarity depends on the total solution volume, not on the volume of solvent alone, which is why solutions are made up to a mark in a volumetric flask rather than by adding a fixed amount of water. And because volume changes with temperature — liquids expand when warmed — the molarity of a fixed amount of solute shifts slightly as the solution heats or cools, so precise work specifies a temperature. The same number, read these different ways, answers strength, comparison, and how to prepare the solution correctly.
The formula is exact, but a couple of practical points are worth keeping in mind.
Total volume, temperature, and consistent units
Molarity is defined per litre of the finished solution, so always use the total solution volume, never the solvent volume alone. Because that volume expands with temperature, a solution's molarity drifts slightly when it is heated or cooled, and published concentrations assume a stated temperature. The result is only meaningful if the amount is in moles and the volume in litres, never a mix — convert millilitres to litres (1000 mL = 1 L) before dividing.