Molarity Calculator
Calculate the molarity of a solution from moles or mass and a volume.
What is Molarity?
Molarity is the concentration chemists use almost everywhere: moles of solute per litre of solution, written mol/L or M. A 0.1 M solution contains 0.1 moles of the substance in every litre — not per litre of water added, which is the distinction that trips people up.
How it works
M = n ÷ V, where V is the volume of the finished solution in litres. If you weighed out a solid, the tool converts the mass to moles first using the formula's molar mass and shows that intermediate, because the grams-to-moles step is where the arithmetic usually goes wrong. Volumes may be given in mL or L.
- Enter what you know. Every field recalculates as you type — there is no submit button. Leave the quantity you want blank and the page solves for it.
- Read the answer and the working. The result appears above the fold; underneath it is the formula with your numbers substituted, so the arithmetic can be checked rather than trusted.
- Check the units and the size. Units are shown on every value and selectable per field, so a result in kJ, kPa or km/h is converted rather than assumed. Sanity-check the magnitude against a known landmark such as 1 g/cm³ for water.
Examples
A textbook problem with a known answer
Every tool here is checked against standard example problems — the molar mass of C6H12O6 is 180.16 g/mol, and free fall from 20 m takes about 2.02 s at g = 9.8 m/s².
A result you want to reason backwards from
Leave the quantity you already know blank instead: given the final answer, most tools recover the starting value — the mass needed for a target concentration, or the height a fall must have had.
Common mistakes
Forgetting that a formula is only as good as its subscripts
H2O and H2O2 are different compounds. The formula field shows its parse — element by element — so a mis-typed subscript is visible before it reaches the arithmetic.
Mixing units in the middle of a calculation
The most common source of a wrong answer is a value in grams next to a formula expecting kilograms, or Celsius next to a gas constant expecting kelvin. This category converts on the way in and labels what it used.
Frequently asked questions
What is the molarity of 5.844 g of NaCl in 500 mL?
0.200 mol/L. NaCl has a molar mass of 58.44 g/mol, so 5.844 g is 0.1000 mol; dividing by 0.500 L gives 0.200 M. Load the example to see the same numbers.
Is molarity the same as molality?
No. Molarity is moles per litre of solution, which changes slightly with temperature as the solution expands; molality is moles per kilogram of solvent, which does not. For work near room temperature they are nearly equal in dilute aqueous solution.
Should the volume be the volume of water I added?
No — it is the volume of the finished solution, made up to the mark in a volumetric flask. Adding solute changes the volume, which is why the distinction matters for accurate work.