Power Calculators

🧪 Molarity Calculator

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Pick what you want to find. The box for that quantity is ignored, so you can leave any number in it.

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📘 About the Molarity

Molarity (M) is the number of moles of solute in one litre of solution. This molarity calculator finds the molarity from the mass you dissolved, or tells you how many grams to weigh out to make a solution of a given molarity.

Enter the volume of the final solution in millilitres — the total volume after making it up to the mark, not the volume of water added.

🧮 Formula

Molarity
M = n ÷ V
From mass
M = m ÷ (Mᵣ × V)
Mass needed
m = M × Mᵣ × V

Where

  • M = molarity (mol/L)
  • n = moles of solute
  • V = volume of solution (L) = mL ÷ 1000
  • m = mass of solute (g)
  • Mᵣ = molar mass of solute (g/mol)
Molarity changes slightly with temperature because volume does. Molality (mol/kg of solvent) does not.

✏️ Worked examples

0.2 M NaCl, 500 mL

You enter
FindMass of solute needed
Molar mass of solute (M)58.44 g/mol
Volume of solution (V)500 mL
Molarity0.2 mol/L
You get
Molarity (mol/L = M)0.2
Mass of solute (g)5.844
Moles of solute (mol)0.1
Concentration (mmol/L)200

Weigh out 5.844 g of sodium chloride and make it up to 500 mL.

Try this example →

4 g NaOH in 250 mL

You enter
FindMolarity
Molar mass of solute (M)40 g/mol
Volume of solution (V)250 mL
Mass of solute4 g
You get
Molarity (mol/L = M)0.40003
Mass of solute (g)4
Moles of solute (mol)0.100008
Concentration (mmol/L)400.03

The solution is 0.40003 M sodium hydroxide.

Try this example →

🧭 How to use this calculator

What you enter

  • FindPick what you want to find. The box for that quantity is ignored, so you can leave any number in it.
  • Molar mass of solute (M) (g/mol)
  • Volume of solution (V) (mL)
  • Mass of solute (g)
  • Molarity (mol/L)

What you get

  • Molarity (mol/L = M)
  • Mass of solute (g)
  • Moles of solute (mol)
  • Concentration (mmol/L)

💡 How to make a solution of known molarity

  • Work out the mass needed: m = M × Mᵣ × V.
  • Weigh the solute and dissolve it in less water than the final volume.
  • Transfer to a volumetric flask and add water up to the mark.
  • Stopper and invert to mix.

❓ Frequently asked questions

What is molarity?

Moles of solute per litre of solution, written mol/L or M.

How do you calculate molarity?

Molarity = moles of solute ÷ volume of solution in litres. Moles = mass ÷ molar mass.

What is the difference between molarity and molality?

Molarity is per litre of solution; molality is per kilogram of solvent.

What does 1 M mean?

One mole of solute in one litre of solution. 1 M NaCl has 58.44 g of NaCl per litre.