Moles of solute per litre of total solution, written M or mol/L. A 1 M NaCl solution has 1 mole — 58.44 g — of NaCl in every litre of finished solution.

How do I make 1 L of 0.5 M NaOH?

0.5 mol/L × 1 L = 0.5 mol needed. NaOH is 40.00 g/mol, so weigh 20.0 g, dissolve it in less than a litre of water, then top up to exactly 1 L.

Is the volume the solvent or the solution?

The total solution. You dissolve the solute in some water, then add water to reach the final mark — that final volume is what molarity uses, not the water you started with.

How do I dilute to a target molarity?

M₁V₁ = M₂V₂. To make 250 mL of 0.1 M from a 1 M stock: V₁ = (0.1 × 250) ÷ 1 = 25 mL of stock, diluted to 250 mL.

What's the difference between molarity and molality?

Molarity is per litre of solution and shifts slightly with temperature as the solution expands. Molality is per kilogram of solvent and doesn't — which is why colligative-property work uses molality.

How do I convert molarity to ppm?

Multiply molarity by the molar mass to get g/L, then by 1,000 for mg/L, which equals ppm for dilute water solutions. 0.001 M NaCl is about 58 ppm.

Molarity Calculator

What molarity tells you

Molarity is the default way chemists state how strong a solution is: moles of dissolved substance per litre of the finished solution. “2 M HCl” means two moles of hydrochloric acid in every litre. Because reactions run on mole ratios, molarity is what lets you scoop out a measured volume of a solution and know exactly how many moles you’re adding — the basis of titrations, reagent dosing, and any calculation done in solution.

The definition hinges on one detail people get wrong: the volume is the total solution, measured after the solute is dissolved and the flask is topped up to the mark. It is not the volume of water you poured in first, which is smaller.

The molarity formula

is molarity in mol/L, is moles of solute, is the solution volume in litres, is the solute mass in grams, and is its molar mass in g/mol. So the calculation is two moves: mass to moles, then moles per litre.

Worked example

The calculator’s defaults are 58.44 g of NaCl (molar mass 58.44 g/mol) dissolved to a 1 L solution.

Moles of solute:

Molarity:

A 1 M sodium chloride solution — one “molar” NaCl.

How to prepare a solution of known molarity

Target	Volume	Moles needed	Grams to weigh
1 M NaCl	1 L	1.000	58.44 g
0.5 M NaOH	1 L	0.500	20.00 g
0.1 M HCl	500 mL	0.050	(dilute stock)
0.25 M glucose	250 mL	0.0625	11.26 g
2 M H₂SO₄	1 L	2.000	(dilute concentrated acid)

Weigh the solute into a volumetric flask, dissolve it in a portion of solvent, then add solvent up to the calibration line — never just add the solute to a full litre.

Molarity Calculator worked example diagram — A visual read of the worked example above — the same numbers the calculator returns for its default inputs.

Where molarity is used

Titration. The unknown’s concentration comes from the known titrant’s molarity and the volumes at the endpoint.
Reaction stoichiometry in solution — moles from molarity × volume, then the equation’s ratio.
Serial dilutions for standards and assays, each step governed by M₁V₁ = M₂V₂.
Buffer and reagent preparation to a specified working concentration.

Common mistakes

Using solvent volume instead of final solution volume.
Adding solute to a full volume of solvent, which overshoots the mark once it dissolves.
Forgetting a solute’s hydration or purity — a 90% pure reagent needs proportionally more mass.
Mixing up molarity and molality in colligative-property problems.

To turn a molar mass and formula into the g/mol you need here, use the molar mass calculator. For the temperature-independent unit, see the molality calculator, and for serial-dilution ratios, the dilution ratio calculator.

Making a solution that isn’t one litre

Find the moles you need from molarity times volume (in litres), then convert to grams. For 250 mL of 0.20 M NaOH (molar mass 40.00 g/mol):

Dissolve 2.00 g of NaOH in some water in a 250 mL volumetric flask, then make it up to the mark.

Diluting a concentrated stock

Use . Diluting 50 mL of 6.0 M HCl to 0.50 M:

So the 50 mL of acid goes into enough water to make 600 mL in total. Add the acid to the water, not the water to the acid. Diluting concentrated acid releases heat, and adding water to acid can make it spatter.

Ion concentrations

Salts that split into several ions give a higher concentration of some ions than of the salt itself. 0.10 M CaCl₂ contains 0.10 M Ca²⁺ but 0.20 M Cl⁻, because each formula unit releases two chloride ions. Use the ion concentration when a problem asks about one particular ion, such as for precipitation or conductivity.

About the formula: Molarity (M) = Moles of solute ÷ Volume of solution (L). Moles = Mass (g) ÷ Molar mass (g/mol).