Molarity Calculator
Molarity is the number of moles of solute per liter of solution. Enter mass and molar mass (or moles directly) plus volume, and this calculator finds the molarity — or solves for any variable you leave blank. Switch to dilution mode to work the M1V1 = M2V2 equation.
How molarity works
When you dissolve a solute in a solvent, molarity measures how crowded the solution is: how many moles of the dissolved substance sit in each liter. Because chemistry happens by the mole (a fixed count of particles), concentrations expressed in moles per liter let you predict exactly how much of one reactant will consume another. If you only know the mass of solute, convert it to moles first by dividing by the molar mass, then divide by the solution volume in liters.
How it’s calculated
Concentration mode uses moles = mass ÷ molar mass, then molarity M = moles ÷ volume(L). It rearranges to mass = M × molar mass × V or V = moles ÷ M when you solve for those. Dilution mode applies M1V1 = M2V2, solving for whichever term is blank — most often V1 = (M2 × V2) ÷ M1, the volume of stock to draw before topping up with solvent.
Assumes the solute fully dissolves and volume refers to total solution volume, not solvent added. Real dilutions can show small volume-contraction effects.
Worked example
Dissolve 10 g of sodium chloride (molar mass 58.44 g/mol) to make 500 mL of solution. Moles = 10 ÷ 58.44 = 0.1711 mol. Molarity = 0.1711 ÷ 0.5 L = 0.342 M. To later dilute that to 0.2 M in 500 mL, you would draw about 293 mL of the 0.342 M stock and add water to 500 mL.
Common mistakes
- Using solvent volume instead of total solution volume — molarity is per liter of finished solution.
- Forgetting to convert milliliters to liters (divide by 1000) before dividing.
- Mixing up molarity (mol/L) with molality (mol per kg of solvent).
- In dilution problems, adding V1 and V2 together instead of topping the stock up to V2.
Where it is used
- Preparing reagents and buffers at a target concentration in the lab.
- Titrations, where known molarities let you find an unknown concentration.
- Pharmaceutical and clinical solution preparation.
- Chemistry coursework converting between mass, moles, and concentration.
Frequently asked questions
What is the formula for molarity?
Molarity (M) equals moles of solute divided by liters of solution: M = n ÷ V. If you know the mass instead of moles, first find moles with n = mass ÷ molar mass, giving M = mass ÷ (molar mass × volume).
How do I make a diluted solution?
Use the dilution equation M1V1 = M2V2, where M1 and V1 are the concentration and volume of the stock and M2 and V2 are the target. Solve for the stock volume you need: V1 = (M2 × V2) ÷ M1, then add solvent up to V2. The dilution mode does this for you.
What units does molarity use?
Molarity is moles per liter (mol/L), abbreviated M. So a 0.5 M solution contains 0.5 moles of solute in every liter of solution. Volume must be the total solution volume, not just the solvent added.
How much salt do I need for a given molarity?
Rearrange to mass = molarity × molar mass × volume. For a 1 M solution of NaCl (molar mass 58.44 g/mol) in 2 liters, you need 1 × 58.44 × 2 = 116.9 grams. Set ‘Solve for’ to Mass and enter the other values.
Is molarity the same as molar mass?
No. Molar mass is the mass of one mole of a substance in grams per mole and is fixed for a given compound. Molarity is a concentration — how many moles are dissolved per liter of solution — and depends on how much you dissolve and in how much liquid.