Molarity Calculator

Moles per litre of solution — not of solvent.

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

Mass of solute

Molar mass

g/mol

58.44 for NaCl, 180.16 for glucose.

Volume of solution

Molarity (mol/L)

1,000 mM · 1 mol

Molarity1 M

In millimolar1,000 mM

Moles of solute1

Mass58.44 g

Volume1 L

Molarity is moles per litre of solution — not of solvent, which is the distinction that trips people. Dissolving something changes the volume, so a 1 M solution is made by dissolving the solute and then topping up to the mark, never by adding it to a full litre of water.

How the Molarity Calculator works

Molarity is moles of solute per litre of solution, and that word matters: dissolving something changes the volume, so a 1 M solution is made by dissolving the solute and topping up to the mark, never by adding it to a full litre of water.

Also known as: molar concentration calculator · moles per litre calculator · how to calculate molarity · molarity formula

Of solution, not of solvent

Molarity is moles per litre of the finished solution. Dissolving something changes the volume, so adding one mole to one litre of water does not give a 1 M solution. It gives slightly more than a litre of something slightly weaker.

The correct method is to dissolve the solute in less than the target volume, then top up to the mark. That is what a volumetric flask is for, and why its neck is narrow.

Molarity against molality

Molality is moles per kilogram of solvent, and the difference matters when temperature changes. Volume expands with heat; mass does not.

So a solution's molarity drifts as it warms while its molality stays fixed. For work at a single temperature molarity is more convenient; across a range, molality is the honest measure.

Where to go next

The Molarity question rarely arrives on its own. These are the ones that usually come with it:

Dilution Calculator — M₁V₁ = M₂V₂, with the diluent volume you actually need.
pH Calculator — pH, pOH and both ion concentrations, on a log scale.
Percent Yield Calculator — Actual over theoretical, and what a figure above 100 means.
Gas Stoichiometry Calculator — Both volumes shown, because the room is not at STP.

Sources

Frequently asked questions

How do I calculate molarity?

Divide the moles of solute by the litres of solution. 58.44 g of sodium chloride is one mole, so in one litre it makes a 1 M solution.

What is the difference between molarity and molality?

Molarity is per litre of solution and molality is per kilogram of solvent. Molality does not change with temperature, since mass does not expand, which is why it is preferred for work across a temperature range.

How do I find moles from grams?

Divide the mass by the molar mass. 29.22 g of a substance with a molar mass of 58.44 g/mol is 0.5 moles.

What does mM mean?

Millimolar — thousandths of a mole per litre. It is the working unit for most of biology, where concentrations are far below 1 M.

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