Molarity relates moles of solute to the volume of a solution. This solves for whichever of the three you need, given the other two.
How it works
Molarity
M = n / V
M is molarity in mol/L, n is moles of solute, V is the total volume of the solution in litres.
Volume of solution, not volume of solvent added
M = n/V uses the total volume of the final solution after the solute is dissolved and the mixture brought up to volume — not the volume of water added beforehand. Dissolving a solid into water and topping up to exactly 1 litre gives a correct molarity; adding the solid to 1 litre of water and letting the final volume land wherever it lands does not, because the solid itself takes up some space too.
How to use this calculator
- Choose which quantity you want solved.
- Enter the other two.
Frequently asked questions
What’s the difference between molarity and molality?
Molarity divides by the volume of the solution; molality divides by the mass of the solvent. They’re numerically close for dilute aqueous solutions but genuinely different quantities, and molality doesn’t change with temperature the way molarity (which depends on volume) does.
Why can’t volume be zero when solving for molarity?
Dividing moles by zero volume is mathematically undefined — there’s no meaningful concentration for a solution with no volume, so this calculator declines rather than returning an infinite number.
How do I make up a solution to a target molarity?
Work out the moles needed (molarity × target volume), convert that to grams using the substance’s molar mass, weigh that mass out, dissolve it, then add solvent up to the target volume — not simply adding that volume of solvent to the solid.
Does this work for any solute?
Yes — the relationship is general. What it doesn’t tell you is the mass in grams; for that, pair the moles result with the molar mass or moles-grams-particles calculators.
Why is this a “solve for” calculator rather than a converter?
Because molarity, moles and volume are three different quantities linked by an equation, not the same quantity expressed differently — the same reasoning behind the “solve for” pattern on Ohm’s Law and density.
