Molarity Calculator
Molarity is moles of solute per litre of solution, so it is one definition read four ways: c = n/V, plus the dilution law M₁V₁ = M₂V₂ that follows from it. Pick the question you have and this returns the answer with the moles it went through on the way. It opens on the standard worked example — 58.44 g of sodium chloride, whose molar mass is 58.44 g/mol, made up to 1 litre, which is exactly 1 mol/L.
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Molarity
1.0000 mol/L
Moles of solute
1.0000 mol
Details
Updates as you typeBoxes this question does not use are ignored, so nothing you typed is lost.
How much solid you have, or are weighing out. 58.44 g of table salt is one mole.
Sum the atomic masses in the formula. NaCl is 22.99 + 35.45 = 58.44 g/mol.
The volume of the finished solution, not the volume of solvent you started with.
Moles of solute per litre of solution. In dilution mode this is the stock you start from.
Dilution mode only: the concentration you want to end up at.
Summary
Molarity
1.0000 mol/L
- Molarity
- 1.0000 mol/L
- Moles of solute
- 1.0000 mol
- Mass of solute
- 58.4400 g
- Solution volume
- 1.0000 L
- Molarity counts litres of finished SOLUTION, not litres of solvent. Dissolve the solid in less water than you need, then make the volume up to the mark — adding the solid to a full litre gives slightly more than a litre and therefore slightly less than the molarity you wanted.
- Molar mass comes from the formula, summed over the periodic table: NaCl is 22.99 + 35.45 = 58.44 g/mol, glucose C₆H₁₂O₆ is 180.16 g/mol, and water is 18.02 g/mol. Getting this wrong scales every answer by the same wrong factor, so it is worth checking first.
- Molarity is per litre of solution and therefore shifts a little with temperature, since the solution expands. Where that matters — precise physical chemistry, or work over a wide temperature range — molality, which is moles per kilogram of solvent, is used instead because mass does not expand.
How this is calculated
- Mass of solute (known)
- 58.4400 g
- Molar mass (known)
- 58.4400 g/mol
- Solution volume (known)
- 1.0000 L
- moles = mass ÷ molar mass
- 1.0000 mol
- molarity = moles ÷ volume
- 1.0000 mol/L
Volume (L)
Compare scenarios
See how one change moves the result
- CurrentYour inputs as they stand1.0000 mol/LCurrent
- Mass of soluteg 73.051.2500 mol/L
- Molar massg/mol 73.050.8000 mol/L
- Solution volumeL 1.250.8000 mol/L
Frequently asked questions
How do I calculate molarity from grams?
Two steps. Divide the mass by the molar mass to get moles, then divide the moles by the volume of solution in litres. Table salt is the cleanest example, because its molar mass in grams per mole is the same number as the mass in the example: 58.44 g of NaCl is 58.44 ÷ 58.44 = 1.000 mol, and one mole made up to one litre is 1.000 mol/L, a 1 M solution. Halve the volume to 500 mL and the same solid gives 2 M.
What does the M in “1 M solution” mean?
It means molar — one mole of solute per litre of solution. IUPAC writes the quantity as c and its unit as mol/dm³, which is the same thing as mol/L, but every bottle and every lab protocol uses M. Watch the case: a small m means molal, moles per kilogram of SOLVENT, which is a different quantity that happens to be numerically close for dilute aqueous solutions.
Is molarity per litre of water or per litre of solution?
Per litre of solution, always. That is why the method is to dissolve the solid in a part of the water first and then make the total volume up to the mark in a volumetric flask, rather than adding the solid to a full litre. Dissolved solid takes up room, so the second method gives you more than a litre and a concentration below the one you were aiming for — noticeably so for concentrated solutions.
How does the dilution formula M₁V₁ = M₂V₂ work?
Adding solvent changes the volume and leaves the amount of solute alone, so the moles before and after are the same number. Moles are molarity times volume on each side, which gives M₁V₁ = M₂V₂ directly. Rearranged, the final volume is M₁V₁ ÷ M₂: one litre of 1 M stock taken to 0.1 M has to end up in ten litres, so you add nine litres of solvent to the litre you already have.
How do I find the molar mass of a compound?
Add up the atomic masses in the formula, taking each element as many times as it appears. Sodium chloride is 22.99 + 35.45 = 58.44 g/mol. Glucose, C₆H₁₂O₆, is 6 × 12.01 + 12 × 1.008 + 6 × 16.00 = 180.16 g/mol. Water is 18.02 g/mol. Hydrates count their water: copper(II) sulfate pentahydrate is 249.68 g/mol, not the 159.61 of the anhydrous salt, and using the wrong one scales every result by the same wrong factor.
What is the difference between molarity and normality?
Molarity counts moles of the compound; normality counts moles of whatever is doing the reacting — protons for an acid, electrons for a redox agent. For hydrochloric acid the two are equal, because each molecule supplies one proton. For sulfuric acid they are not: 1 M H₂SO₄ is 2 N, since each molecule can give up two. Normality is falling out of use precisely because it depends on which reaction you have in mind.