Molarity Calculator

Last updated: June 2026

Use this molarity calculator to calculate the concentration of a solution from the amount of solute and the volume of solution. It is written for O-Level, IGCSE, A-Level and Singapore H2 Chemistry students who need to handle concentration, dilution and titration calculations carefully.

Key takeaway: Molarity is the amount of solute in one unit volume of solution. In school chemistry, concentration is often calculated using c = n / V, where volume must usually be converted from cm3 to dm3.

What is molarity?

Molarity is a way of measuring the concentration of a solution. It tells us how many moles of solute are present in a given volume of solution.

For example, a 1.00 mol dm−3 sodium chloride solution contains 1.00 mol of sodium chloride in every 1.00 dm3 of solution.

The word molarity is commonly used in many chemistry resources. In Singapore and UK-style exam questions, you will often see the term concentration instead, with the unit mol dm−3.

Molarity formula

The main formula is:

c = n / V

where c is concentration in mol dm−3, n is the amount of solute in mol, and V is the volume of solution in dm3.

Rearranging the formula gives:

n = cV

This version is especially common in titration calculations.

Volume conversion

The most common mistake in molarity questions is using cm3 directly in the formula. If the concentration is in mol dm−3, the volume must be in dm3.

1000 cm3 = 1 dm3

So:

25.0 cm3 = 25.0 / 1000 = 0.0250 dm3

250 cm3 = 250 / 1000 = 0.250 dm3

Calculating molarity from mass

Sometimes the question gives mass instead of moles. In that case, first calculate the amount of substance using:

n = m / Mr

Then use:

c = n / V

This means a molarity calculation often has two steps: convert mass to moles, then divide by volume.

Worked examples

Example 1: Finding molarity from moles and volume

Calculate the concentration of a solution containing 0.100 mol of sodium hydroxide in 250 cm3 of solution.

First convert the volume:

250 cm3 = 0.250 dm3

Then use c = n / V:

c = 0.100 / 0.250 = 0.400 mol dm−3

Therefore, the concentration of the sodium hydroxide solution is 0.400 mol dm−3.

Example 2: Finding molarity from mass and volume

5.85 g of sodium chloride is dissolved in water and made up to 500 cm3 of solution. Calculate the concentration of the solution.

Mr of NaCl = 23.0 + 35.5 = 58.5

First calculate moles:

n = 5.85 / 58.5 = 0.100 mol

Then convert the volume:

500 cm3 = 0.500 dm3

Finally calculate concentration:

c = 0.100 / 0.500 = 0.200 mol dm−3

Common exam traps

Trap 1: Do not use cm3 directly in c = n / V if concentration is in mol dm−3. Convert cm3 to dm3 first.
Trap 2: Do not confuse mass concentration with molar concentration. g dm−3 and mol dm−3 are different units.
Trap 3: In titration questions, use the mole ratio from the balanced equation. Do not assume the reacting ratio is always 1:1.
Trap 4: If the solution is made up to a final volume, use the final volume of the solution, not just the volume of water added.

Frequently Asked Questions

Is molarity the same as concentration?

Molarity is a type of concentration. It specifically refers to concentration measured in mol per unit volume, commonly mol dm−3 in school chemistry.

What is the unit of molarity?

The common unit is mol dm−3. You may also see mol L−1, which is numerically equivalent because 1 dm3 is the same as 1 L.

When should I use n = cV?

Use n = cV when the question gives concentration and volume, and you need to find the amount of substance in moles. This is very common in titration and dilution questions.

Why must cm3 be converted to dm3?

Because mol dm−3 means moles per dm3. If you use cm3 directly, your answer will usually be 1000 times too large or too small.

Can this calculator be used for titration?

Yes, it can help with the concentration part of titration calculations. However, titration questions also require the mole ratio from the balanced equation, so the Titration Calculator is better for full titration problems.

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