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Molarity Calculator

Find the molarity of a solution from mass, molar mass and volume, or the mass you need to make a solution of a set molarity.

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Volume is the final volume of the whole solution, not the volume of water added. Molar mass is found on a periodic table or a chemical’s label.

Quick Answer

Molarity (M) is moles of solute per liter of solution: M = moles ÷ liters. Moles = mass ÷ molar mass. So 5.844 g of table salt (NaCl, 58.44 g/mol) in 500 mL of solution is 0.1 mol ÷ 0.5 L = 0.2 M.

Last updated: 2 November 2026 ·How we calculate this: molarity and mole formulas

Table of Contents

How This Molarity Calculator Works

Molarity tells you how concentrated a solution is. Choose whether to find the molarity or the mass of solute you need. The calculator converts milliliters to liters, works out the moles, and shows each step.

Quick explanation: molarity = moles of solute ÷ liters of solution.

  • Solute: the substance being dissolved, such as salt.
  • Molar mass: grams per mole, from the periodic table.
  • Volume: the final volume of solution, in mL.

How to Use the Molarity Calculator

  1. Choose whether to find the molarity or the mass of solute needed.
  2. Enter the molar mass of the solute in g/mol.
  3. Enter the final volume of the solution in mL.
  4. Enter the mass of solute, or the target molarity, depending on your choice.
  5. Press Calculate to see the molarity, moles, mass and steps.

Core Formulas

  • Molarity: M = n ÷ V
  • Moles: n = mass ÷ molar mass
  • Mass needed: mass = M × V × molar mass
  • Dilution: M₁ × V₁ = M₂ × V₂

n is moles, V is volume in liters, and M is in mol/L, also written as M.

Key Terms

  • Mole: an amount of substance containing about 6.022 × 10²³ particles.
  • Molar mass: the mass of one mole of a substance, in g/mol.
  • Solute: the substance dissolved in a solution.
  • Solvent: the liquid that does the dissolving, often water.
  • Concentration: how much solute is present in a given amount of solution.

Worked Example

How much glucose (C₆H₁₂O₆, 180.16 g/mol) do you need for 250 mL of a 0.5 M solution?

  • Volume = 250 ÷ 1,000 = 0.25 L
  • Moles = 0.5 × 0.25 = 0.125 mol
  • Mass = 0.125 × 180.16 = 22.52 g

Real-Life Examples

  • Saline solution: 9 g of NaCl in 1 L of solution is 9 ÷ 58.44 = 0.154 M, close to the strength of normal saline.
  • A lab stock: to make 100 mL of 1 M NaOH (40.00 g/mol), weigh out 4.00 g.
  • Diluting a stock: to make 500 mL of 0.1 M from a 2 M stock, use M₁V₁ = M₂V₂: V₁ = 0.1 × 500 ÷ 2 = 25 mL of stock, topped up to 500 mL.
  • Sugar in water: 34.2 g of sucrose (342.3 g/mol) in 250 mL is about 0.4 M.

Molarity vs Molality

  • Molarity (M): moles of solute per liter of solution. Easy to measure with glassware.
  • Molality (m): moles of solute per kilogram of solvent. It does not change with temperature.
  • When they differ: for dilute water solutions they are close, but they drift apart for strong solutions.

Molar Masses of Common Compounds

CompoundFormulaMolar mass (g/mol)
WaterH₂O18.02
Sodium chlorideNaCl58.44
Sodium hydroxideNaOH40.00
Hydrochloric acidHCl36.46
GlucoseC₆H₁₂O₆180.16
SucroseC₁₂H₂₂O₁₁342.30
Calcium carbonateCaCO₃100.09

Lab Tips

  • Use a volumetric flask: dissolve the solute, then fill to the line.
  • Check for hydrates: a compound with water of crystallization has a higher molar mass.
  • Temperature: volume changes slightly with temperature, which can affect molarity.
  • Safety: follow your lab’s rules and read the safety data sheets first.

Common Mistakes to Avoid

  • Using mL instead of L. Divide mL by 1,000 before dividing moles by volume.
  • Using the water volume. Molarity uses the final solution volume.
  • Wrong molar mass. Check the full formula, including any water of hydration.
  • Mixing up M and m. Molarity is per liter of solution, molality is per kilogram of solvent.
  • Rounding too early. Keep extra digits until the final answer.

Frequently Asked Questions

Divide the moles of solute by the volume of solution in liters. If you know the mass, first divide it by the molar mass to get moles.

Moles per liter (mol/L), written as M.

Divide grams by molar mass to get moles, then divide by liters of solution.

A solution with 1 mole of solute in every liter of solution.

Use M₁V₁ = M₂V₂. Solve for the volume of stock solution, then add solvent up to the final volume.

One thousandth of a mole per liter. 0.2 M is 200 mM.

Add up the atomic masses of every atom in the formula from a periodic table. For NaCl, 22.99 + 35.45 = 58.44 g/mol.

Normality counts reacting units, such as hydrogen ions in an acid. For HCl they are the same, but for H₂SO₄ normality is twice the molarity.

Multiply molarity by molar mass. A 0.2 M NaCl solution has 0.2 × 58.44 = 11.69 g per liter.

A solution whose concentration is known accurately, often used to measure other samples in titrations.

Slightly, because liquids expand and contract, which changes the volume.

References & Sources

SourceUsed ForLink
Wikipedia, Molality How molality differs from molarity. https://en.wikipedia.org/wiki/Molality
Wikipedia, Molar concentration Molarity formulas and units. https://en.wikipedia.org/wiki/Molar_concentration