How do you calculate molarity?

Divide moles of solute by litres of solution. 0.25 mol in 500 mL: 0.25 ÷ 0.5 = 0.5 M. If you have grams, divide by the molar mass first: 10 g of NaOH (40.00 g/mol) is 0.25 mol. Enter either and the page shows both steps.

How do I make a 1 M solution?

Weigh out one molar mass in grams — 58.44 g for NaCl — dissolve it in less than a litre of water, then add water to bring the total volume to exactly 1 L. For 250 mL, use a quarter of the mass, 14.61 g.

What is the difference between molarity and molality?

Molarity is moles per litre of solution; molality is moles per kilogram of solvent. For dilute water solutions the two are nearly equal (a litre of water is a kilogram); they diverge for concentrated solutions and at other temperatures.

What does 0.5 M or 5 mM mean?

0.5 M means 0.5 moles of solute in every litre of solution; 5 mM is 0.005 moles per litre, or 5 millimoles. The M is read 'molar'. A 0.5 M NaCl solution contains 29.22 g of NaCl per litre.

How do I make 250 mL of a 0.1 M solution?

Moles needed = 0.1 × 0.25 = 0.025 mol. For sodium chloride that is 0.025 × 58.44 = 1.46 g, dissolved and made up to 250 mL in a volumetric flask.

Molarity Calculator (from Moles or Grams, L or mL)

Molar concentration from moles or grams of solute and the solution volume, with the working and the value in mM.

Inputs

I know the solute's

Moles of solute(mol)

0 mol1,000,000,000 mol

Mass of solute (grams mode)(g)

0 g1,000,000,000 g

Molar mass of solute (grams mode)(g/mol)

0.001 g/mol1,000,000 g/mol

Solution volume

01,000,000

Volume unit

Include CalculateEveryday mark

Molarity

0.3746 mol/L

Working: 0.133 mol ÷ 355 mL (0.355 L) = 0.3746 mol/L
In millimolar: 374.6479 mM
Moles of solute: 0.133 mol
Volume: 0.355 L

Use this calculator on your own site

Free embed

Two lines of HTML, unlimited views
Shows a small CalculateEveryday bar, with a credit link under the calculator

What each Molarity input means

I know the solute's: Whether you know the amount of solute in moles, or its mass in grams (the page then divides by the molar mass).
Moles of solute: Moles of solute, if you have them.
Mass of solute (grams mode): Grams of solute, if you weighed it out.
Molar mass of solute (grams mode): The solute's molar mass in g/mol — 58.44 for NaCl, 180.16 for glucose. The molar mass calculator finds it from a formula's atomic masses.
Solution volume: The volume of the finished solution — not of the water added, since the solute takes up room too.
Volume unit: Litres or millilitres; millilitres are divided by 1,000.

Molarity formula

M = moles of solute ÷ litres of solution · moles = mass (g) ÷ molar mass (g/mol) · mL ÷ 1,000 = L · 1 M = 1,000 mM

M = \frac{n_{\text{solute}}}{V_{\text{solution}}\ (\text{L})}, \qquad n = \frac{m}{\mathcal{M}}

Molarity is the number of moles of dissolved substance in each litre of solution. Count the moles — directly, or as the mass in grams divided by the molar mass — and divide by the volume of the finished solution in litres, converting from millilitres by dividing by 1,000. The volume is of the whole solution, not of the solvent added, because dissolving something changes the volume slightly; that is why a volumetric flask is filled to the line after the solute is in. The page takes either moles or grams plus a molar mass, accepts litres or millilitres, shows the division, and gives the result in millimolar as well, since biology works in mM and µM.

Molarity worked example

OpenStax's Example 3.14: a 355 mL soft drink containing 0.133 mol of sucrose. Convert the volume, 355 ÷ 1,000 = 0.355 L, and divide: 0.133 ÷ 0.355 = 0.375 mol/L, or 375 mM. Starting from grams instead — 29.22 g of NaCl at 58.44 g/mol in 1 L — the moles are 29.22 ÷ 58.44 = 0.5, so the solution is 0.5 M.

More Molarity examples

29.22 g of sodium chloride made up to 500 mL: 29.22 ÷ 58.44 = 0.5 mol, and 0.5 ÷ 0.5 L gives a molarity of 1 mol/L — 1 M, or 1,000 mM.

0.25 mol of solute in 2 L of solution: 0.25 ÷ 2 = 0.125 mol/L, or 125 mM.

Where the Molarity calculator can give the wrong answer

Volume means the final solution, not the water used. Dissolving 58 g of salt in 1 L of water gives slightly more than 1 L and a molarity slightly under 1 M; make the solution up to the mark instead.
Molarity changes with temperature because volume does; molality (moles per kilogram of solvent) does not, which is why it is used for boiling-point and freezing-point work.
The molar mass has to be for the substance as weighed. A hydrated salt such as CuSO₄·5H₂O has a molar mass of 249.7 g/mol, not the 159.6 of anhydrous CuSO₄, and using the wrong one puts the molarity out by a third.
Grams of an impure or wet solid overstate the moles. Analytical work corrects for purity; this page assumes what you weighed is what you meant.
Very small concentrations are usually written in mM or µM to avoid strings of zeros; the page shows mM for that reason.

Spotted a mistake? Tell us

Molarity reference table

Grams needed for 1 litre of a 1 M solution
Compound	Formula	Molar mass (g/mol) — grams for 1 L of 1 M
Sodium hydroxide	NaOH	40.00
Sodium chloride	NaCl	58.44
Potassium chloride	KCl	74.55
Calcium chloride	CaCl₂	110.98
Glucose	C₆H₁₂O₆	180.16
Copper(II) sulfate pentahydrate	CuSO₄·5H₂O	249.69
Sucrose	C₁₂H₂₂O₁₁	342.30

Source: Molar masses from IUPAC standard atomic weights; for any other molarity or volume, grams = M × L × molar mass

Molarity FAQ

: Divide moles of solute by litres of solution. 0.25 mol in 500 mL: 0.25 ÷ 0.5 = 0.5 M. If you have grams, divide by the molar mass first: 10 g of NaOH (40.00 g/mol) is 0.25 mol. Enter either and the page shows both steps.
: Weigh out one molar mass in grams — 58.44 g for NaCl — dissolve it in less than a litre of water, then add water to bring the total volume to exactly 1 L. For 250 mL, use a quarter of the mass, 14.61 g.
: Molarity is moles per litre of solution; molality is moles per kilogram of solvent. For dilute water solutions the two are nearly equal (a litre of water is a kilogram); they diverge for concentrated solutions and at other temperatures.
: 0.5 M means 0.5 moles of solute in every litre of solution; 5 mM is 0.005 moles per litre, or 5 millimoles. The M is read 'molar'. A 0.5 M NaCl solution contains 29.22 g of NaCl per litre.
: Moles needed = 0.1 × 0.25 = 0.025 mol. For sodium chloride that is 0.025 × 58.44 = 1.46 g, dissolved and made up to 250 mL in a volumetric flask.