Molarity Calculator

Calculate molarity from moles and solution volume, or from grams and molecular weight.

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Solute mass (g)

Molecular weight (g/mol)

Moles (optional)

Solution volume (L)

Result

Enter values to calculate.

Summary

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Detail

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Calculate the molarity of a solution from moles and volume, or directly from solute mass and molecular weight, for chemistry coursework and lab prep.

How It Works

How Molarity Calculator Works

Molarity is defined as moles of solute divided by liters of solution: M = mol ÷ L. If you already know the number of moles, enter it directly along with the solution volume.

If you only know the mass of solute (in grams) and its molecular weight (in g/mol), the calculator first converts mass to moles using moles = grams ÷ molecular weight, then divides by the solution volume to get molarity.

Worked Example

See It In Action

Dissolving 58.44 g of sodium chloride (molecular weight 58.44 g/mol) in enough water to make 2 L of solution gives 58.44 ÷ 58.44 = 1 mole, and 1 mol ÷ 2 L = a molarity of 0.5 M.

Real-World Use Cases

Who Uses Molarity Calculator and Why

Preparing a solution of a known concentration for a chemistry lab experiment.
Working backward from a desired molarity to figure out how much solute mass to weigh out.
Checking a lab prep calculation before mixing a solution, to avoid wasting reagent on an incorrect concentration.
Completing a chemistry coursework problem that gives solute mass, molecular weight, and volume.

Common Mistakes

Mistakes to Avoid

Entering solution volume in milliliters without converting to liters first — molarity is defined per liter, so an unconverted milliliter figure (like 500 instead of 0.5) throws the result off by 1,000x.
Filling in both the moles field and the mass/molecular-weight fields at once, when only one path (direct moles, or mass ÷ molecular weight) should be used per calculation.
Treating molarity as interchangeable with other concentration measures like molality or mass percent — they're related but not numerically the same, and mixing them up in a lab context can lead to a genuinely wrong concentration.

Pro Tips

Tips for Best Results

If you know moles directly, skip the mass and molecular weight fields entirely and enter moles straight into the calculation.
Always convert milliliters to liters (divide by 1,000) before entering solution volume, since molarity is defined as moles per liter.

Troubleshooting

Fixing Common Problems

My molarity result is 1,000 times too high or too low. — Check your volume units — this almost always means milliliters were entered where liters were expected (or vice versa); divide a milliliter figure by 1,000 before entering it.

I don't know the molecular weight of my solute. — Use the Molecular Weight Calculator to work it out from the chemical formula first, then bring that figure back here.

Glossary

Terms Explained

Molarity (M): A measure of solution concentration defined as moles of solute per liter of solution.

Mole: A unit representing a fixed number of particles (Avogadro's number, about 6.022×10²³) of a substance, used to relate mass to molecular-scale quantities.

FAQ

Frequently Asked Questions

What if I know moles directly instead of mass?

Enter the moles value directly — the calculator uses it instead of computing moles from mass and molecular weight, so you can skip those two fields.

What units does the volume need to be in?

Solution volume must be entered in liters. If you measured in milliliters, divide by 1,000 first (e.g., 500 mL = 0.5 L).

Is molarity the same as concentration?

Molarity is one specific way to express concentration (moles per liter). Other measures like molality, mass percent, or parts per million describe concentration differently and are not interchangeable with molarity without a conversion.