How to calculate molarity
Molarity tells you how concentrated a solution is by counting how many moles of solute are dissolved in each liter of solution. The defining equation is M = moles of solute / liters of solution. Because it is a simple ratio, rearranging it lets you solve for whichever quantity you are missing: moles = M × liters and liters = moles / M.
This calculator detects which field you leave blank in the moles mode and solves for it automatically. Volumes can be entered in liters or milliliters — millilitre values are divided by 1000 to convert to liters before the formula is applied, so the result is always in moles per liter.
If you only know the mass of your solute, switch to mass mode. The tool first finds moles with moles = mass (g) / molar mass (g/mol), then applies M = moles / liters. To go the other way and dilute a concentrated stock solution to a lower concentration, see the dilution calculator, which uses C1V1 = C2V2.
Reference note: this is a neutral chemistry-math tool. Molarity uses the total volume of the finished solution, not the volume of solvent added. Volume changes slightly with temperature, so for temperature-independent work consider molality instead. Always follow your own institution's safety procedures.
Frequently asked questions
- What is molarity?
- Molarity is the concentration of a solution measured as moles of solute per liter of solution. It uses the symbol M, so a 1 M solution has 1 mole of solute in every liter. The defining equation is M = moles / liters.
- How do I calculate molarity?
- Divide the moles of solute by the volume of solution in liters: M = moles / liters. For example, 2 moles in 0.5 L gives 2 / 0.5 = 4 M. If your volume is in milliliters, divide by 1000 to convert to liters first.
- What units is molarity in?
- Molarity is measured in moles per liter, written mol/L or M (molar). The top of the ratio is always moles of solute and the bottom is always liters of total solution, so milliliter volumes must be converted to liters.
- How do I find moles from mass?
- Divide the mass of solute by its molar mass: moles = mass (g) / molar mass (g/mol). For example, 58.44 g of NaCl (molar mass ≈ 58.44 g/mol) is 1 mole, which you can then put into M = moles / liters.
- What is the difference between molarity and molality?
- Molarity (M) is moles per liter of solution and depends on volume, which shifts a little with temperature. Molality (m) is moles per kilogram of solvent and stays constant with temperature. This tool calculates molarity.
- How do I make a 1 M solution?
- Weigh out one mole of solute (a mass in grams equal to its molar mass), dissolve it in some solvent, then add solvent until the total volume is exactly 1 liter. For NaCl that is about 58.44 g made up to 1 L.