Calculators
Molarity Calculator
Find the molarity, solute mass, solution volume, or moles of solute with common molar mass presets, locally in your browser.
Enter the solute mass, molar mass, and solution volume to find the molarity, or solve for the mass, volume, or moles instead. Calculations run locally in your browser; your values are not uploaded or stored.
Solve M = mass / (molar mass × volume) for any variable.
Molarity is the number of moles of solute per litre of solution, written M or mol/L. Enter the solute mass in grams, milligrams, or kilograms, the solution volume in millilitres or litres, and the molar mass of the solute in grams per mole, and the calculator reports the molarity in mol/L and mmol/L along with the moles of solute, the mass, and the volume. Switch the “Solve for” option to find the solute mass needed for a target concentration, the solution volume a given mass will make, or the moles in a weighed sample. Ten common laboratory presets, from water at 18.015 g/mol to potassium permanganate at 158.034 g/mol, fill the molar mass field, or enter your own between 0.001 and 10,000,000 g/mol. For example, 58.44 g of sodium chloride (molar mass 58.44 g/mol) made up to 1 L gives 1.000 mol/L, and 20 g made up to 500 mL gives about 0.684 mol/L. The result assumes the solute fully dissolves and the solution is made up to the stated final volume, not that the volume is added to the solvent. All calculations run locally in your browser; your values are not uploaded or stored.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
How does the molarity calculator work?
It uses the definition of molarity: M = moles of solute / litres of solution, with moles = mass / molar mass, so M = mass / (molar mass x volume). For example, 58.44 g of sodium chloride (molar mass 58.44 g/mol) made up to 1 L is 58.44 / (58.44 x 1) = 1.000 mol/L. Switch the “Solve for” option to rearrange the same equation for the solute mass (mass = molarity x molar mass x volume), the solution volume (volume = mass / (molar mass x molarity)), or the moles of solute (moles = mass / molar mass).
What is molarity?
Molarity is the concentration of a solution expressed as moles of solute per litre of solution, with the unit mol/L and the symbol M. A 1 M (one molar) sodium chloride solution contains one mole of NaCl, 58.44 g, in every litre of finished solution. Related measures include mass concentration in g/L and molarity’s temperature-independent sibling, molality (moles per kilogram of solvent).
What is the difference between molarity and molality?
Molarity counts moles of solute per litre of solution, so it changes slightly with temperature because solutions expand and contract. Molality counts moles per kilogram of solvent, which does not change with temperature, so molality is preferred for precise work across temperature ranges. For dilute aqueous solutions near room temperature the two numbers are very close.
How do I find the molar mass of a solute?
Add up the standard atomic masses of every atom in the chemical formula, in g/mol. The preset list covers common laboratory chemicals such as water (18.015), sodium chloride (58.44), glucose (180.156), and sodium hydroxide (40.00). For hydrated compounds include the water molecules, for example copper(II) sulfate pentahydrate, CuSO4·5H2O, is about 249.68 g/mol. If you only have the mass of a sample and its formula weight, the “Moles of solute” mode gives the answer directly.
Does dissolving a solid change the volume of the solution?
Usually, yes, slightly. Molarity refers to the final volume of the solution, not the volume of solvent you started with: 58.44 g of NaCl dissolved in exactly 1 L of water makes slightly more than 1 L of solution. For accurate work, dissolve the solute first, then bring the solution up to the mark in a volumetric flask. This calculator assumes the stated volume is the finished solution volume; it is an educational tool, not a substitute for laboratory procedure or safety guidance, and all calculations run locally in your browser.