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True Calculator

Molarity Calculator

Calculate molarity, moles and g/L concentration from solute mass, molecular weight and solution volume.

g
g/mol

Use the molecular weight calculator for the formula.

L

Molarity

1 M

Moles of solute per litre of solution

Moles of solute

0.5

Concentration

58.44 g/L

Molarity = mass ÷ molecular weight ÷ volume. Always dissolve the solute fully and make the volume up to the mark for accurate results.

Last updated: January 2026

How this calculator is verified

Checked by True Calculator automated test suite on

  • Formula verified against a published worked example in the automated test suite
  • Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests

The full verification method is on our how we verify page. Found an error? Tell us and we will re-check it.

When to Use This Calculator

Use this calculator whenever a recipe, practical class or lab protocol calls for a solution of known molarity. Indian undergraduate labs run on these calculations daily — preparing 0.1 M KMnO₄ for titration, 1 M NaOH for neutralisation experiments, or standard glucose solutions for biochemistry practicals. Beyond the classroom, molarity matters in water treatment dosing, fertiliser solution preparation for hydroponic farming, and in pathology labs where reagent concentrations must be exact. The moles readout is equally valuable in stoichiometry problems, letting you check how much product a given mass of reactant should produce. Enter the numbers once and verify every step before the chemicals hit the bench.

How to Use This Calculator

  1. Step 1: Weigh the solute and enter its mass in grams.
  2. Step 2: Enter the molecular weight in g/mol — use the molecular weight calculator to find it from the formula.
  3. Step 3: Enter the final solution volume in litres, not the water you started with.
  4. Step 4: Read the moles of solute and the molarity, and check the g/L concentration for labelling.

Worked Example

To prepare a 1 M sulphuric acid solution: take 49.04 g of H₂SO₄, whose molecular weight is 98.08 g/mol. That is 49.04 ÷ 98.08 = 0.5 moles. Dissolve it and make the final volume exactly 0.5 L, and the molarity is 0.5 ÷ 0.5 = 1 M. The same logic gives 1 M NaCl from 29.22 g of salt (58.44 g/mol) made up to 0.5 L — a stock solution used constantly in Indian school and college labs.

Tips and Common Mistakes

  • •Make the volume up to the mark in a volumetric flask — adding water in two stages is never as accurate.
  • •For concentrated acids, always add acid to water slowly with stirring, never the reverse.
  • •Use distilled or deionised water; tap water adds ions that change the real concentration.
  • ✗Do not measure the volume before dissolving — the solute adds volume and shifts the molarity.
  • ✗Do not forget the molecular weight of hydrates (like CuSO₄·5H₂O) includes the water of crystallisation.

Frequently Asked Questions

What is molarity?

Molarity (M) is the number of moles of solute dissolved in one litre of solution. Dissolving 29.22 g of NaCl (molecular weight 58.44 g/mol) in 0.5 L of water gives 0.5 mol ÷ 0.5 L = 1 M solution.

How is molarity calculated?

Moles = mass ÷ molecular weight, then molarity = moles ÷ volume in litres. For 29.22 g of NaCl in 0.5 L: 29.22 ÷ 58.44 = 0.5 mol, and 0.5 ÷ 0.5 = 1 M.

What is the difference between molarity and molality?

Molarity uses litres of solution; molality uses kilograms of solvent. Molarity changes slightly with temperature because solutions expand, while molality does not. For lab work at room temperature the two are close.

Why do I need the molecular weight?

Molecular weight (g/mol) converts mass to moles, and moles are what molarity counts. Use the molecular weight calculator to work it out from the chemical formula — NaCl is 58.44 g/mol.

How do I make up a 1 M solution?

Weigh the required solute, dissolve it in less than the final volume of distilled water, then top up to the mark in a volumetric flask so the total is exactly 1 litre. Always add acid to water, never water to acid.

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