Molarity Calculator
Find the molar concentration of any solution by entering moles of solute and solution volume. Essential for lab prep, titrations, and stoichiometry problems.
About this calculator
Molarity (M) measures how many moles of a solute are dissolved in one liter of solution. It is the most common unit of concentration in chemistry. The formula is M = moles / volume, where moles is the amount of solute in mol and volume is the total solution volume in liters. A higher molarity means a more concentrated solution. Molarity is temperature-dependent because liquid volume can expand or contract, so measurements are typically made at a standard temperature. Knowing molarity is essential for preparing reagents, performing titrations, and calculating reaction stoichiometry accurately.
How to use
Suppose you dissolve 0.5 mol of NaCl into enough water to make 2 L of solution. Enter moles = 0.5 mol and volume = 2 L. The calculator applies M = moles / volume = 0.5 / 2 = 0.25 M. Your sodium chloride solution has a molarity of 0.25 M, meaning there are 0.25 moles of NaCl in every liter of solution. Adjust the volume or moles fields to explore how concentration changes.
Frequently asked questions
What is the difference between molarity and molality?
Molarity (M) expresses moles of solute per liter of solution, while molality (m) expresses moles of solute per kilogram of solvent. Molarity is volume-based and therefore changes slightly with temperature as liquids expand. Molality is mass-based and remains constant regardless of temperature changes. For most room-temperature lab work, molarity is the preferred unit, but molality is essential for colligative property calculations like boiling point elevation.
How do I convert grams to moles before using the molarity calculator?
To convert grams to moles, divide the mass of your solute by its molar mass (found on a periodic table or chemical formula). For example, NaCl has a molar mass of 58.44 g/mol, so 29.22 g of NaCl equals 29.22 / 58.44 = 0.5 mol. Once you have moles, you can enter it directly into this calculator along with your solution volume to find molarity. This two-step process is fundamental to virtually every solution-preparation task in chemistry.
Why does molarity use the volume of solution rather than the volume of solvent?
Molarity is defined per liter of total solution, not per liter of pure solvent, because adding solute changes the total volume of the liquid. For example, dissolving a large amount of sugar in 900 mL of water might yield 1 L of solution, not 1.9 L. Using solution volume ensures a consistent and reproducible concentration standard. This distinction matters most when preparing precise standard solutions in volumetric flasks, where you add solvent up to the calibration mark after adding the solute.