The formula
How it works
Molarity measures how concentrated a solution is — the number of moles of a dissolved substance per litre of solution. Because molarity, moles and volume are tied by one formula, you can enter any two and solve for the third.
FAQ
What exactly is a mole?
A mole is a fixed count of particles — about 6.022 × 10²³ of them. It lets chemists weigh out a known number of molecules, so concentrations can be compared no matter the substance.
How do I get moles from grams?
Divide the mass in grams by the substance’s molar mass in grams per mole. For example, 58.5 g of table salt is one mole, because its molar mass is about 58.5 g/mol.
What happens to molarity when I dilute a solution?
Adding solvent increases the volume without adding more solute, so the molarity drops proportionally — this relationship is captured by the dilution equation \(M_1V_1 = M_2V_2\).
Is molarity the same as concentration in general?
Molarity is one specific way to express concentration — moles per litre — but concentration can also be given as mass per volume, percent by mass, or parts per million, so always check which unit is being used.
Does temperature affect molarity?
Yes, slightly — because molarity is based on solution volume, and volume can expand or contract with temperature, the same solution can have a marginally different molarity when measured hot versus cold.
What is molality and how does it differ from molarity?
Molality measures moles of solute per kilogram of solvent rather than per litre of solution, so unlike molarity it does not change with temperature since mass, not volume, is used.
Can molarity be calculated for any substance dissolved in any solvent?
Yes — the formula \(M = n/V\) applies regardless of what is dissolved or what the solvent is, as long as you know the moles of solute and the total solution volume.
About the molarity calculator
This calculator finds the molarity of a solution, or works backwards to the moles of solute or the volume, from the other two. Molarity is the most common way chemists describe concentration: it counts how many moles of a dissolved substance sit in each litre of solution. Because it is based on a fixed number of particles rather than mass, molarity lets very different chemicals be mixed and compared in the right proportions.
How to use it
Pick what you want to find with the “Solve for” menu, then enter the other two values. To find molarity, enter the moles of solute and the volume of solution in litres: 0.5 moles dissolved in 1 litre gives a molarity of 0.5 mol/L. Choose Moles or Volume to rearrange the formula instead — useful when you know the concentration you want and need to work out how much solute to weigh out or how much water to add.
The formula
Molarity is moles of solute divided by litres of solution, , where is the molarity, is the amount in moles and is the volume in litres. Because it is a simple ratio it rearranges to for the moles needed and for the volume. If you start from a mass, first convert to moles by dividing by the molar mass, then use this formula.
Where it is used
Molarity is the working language of the chemistry lab. It is used to prepare solutions of a known strength, to scale reactions up or down, and to calculate how reactants combine in the right amounts. Biologists use it for buffers and growth media, medicine uses it for drug concentrations and IV fluids, and industry uses it in quality control. Any time a substance is dissolved and its strength matters, molarity is how that strength is measured.