How this calculator works
- Step 1Molesmass ÷ molar massTurn grams into moles if needed.
- Step 2LitresmL ÷ 1000Use the volume of the whole solution.
- Step 3Molaritymol ÷ LMoles per litre, written M.
Molarity tells you how much substance is dissolved in each litre of solution. A 1 M solution has one mole in every litre.
Worked example: vinegar
- Molarity
(mass ÷ molar mass) ÷ litres
- Moles25.2 g ÷ 60.052 g/mol0.4196 mol
- Litres500 mL ÷ 10000.500 L
- Molaritymoles ÷ litres0.839 M
The textbook gives 0.839 M.
Dilution
- Sucrose in a drink0.375 M0.133 mol in 355 mL (Example 3.14).
- Diluted Cu(NO₃)₂2.36 M850 mL of 5.00 M made up to 1.80 L (Example 3.19).
Diluting adds solvent, not solute: the moles stay the same, so C₁V₁ = C₂V₂.
Assumptions and limits
- Final volumeVolume of the solution, not the water used.
- Additive volumesReal mixtures can shrink slightly.
- Your molar massEnter it from the formula or label.
- Not for medicinesUse lab procedures for real preparations.
Related chemistry tools
Molarity needs moles. Molar mass turns grams into moles.
To find a compound’s molar mass, use the molecular weight calculator. For acidity from concentration, try the pH calculator, and for gases, the ideal gas law calculator.
Common mistakes
Mistake: Dividing by millilitres.
Instead: Convert to litres first.
Mistake: Using the water volume.
Instead: Use the total solution volume.
Mistake: Using grams as moles.
Instead: Divide by the molar mass.
Checking the method
A separate script re-works every golden value in millimoles per millilitre with exact fractions, and reproduces the three OpenStax examples.
Read how we test our calculators, or browse more maths calculators.