How the molarity calculator works
Molarity (M) is the number of moles of solute per liter of final solution. Moles come from dividing the mass of a substance by its molar mass, the mass of one mole found by adding atomic masses from the periodic table.
Molarity M = n ÷ volume of solution (L)
Mass needed = M × V × molar mass
Use the total volume of the finished solution, not the volume of water added: dissolve the solute, then top up to the mark in a volumetric flask. Molarity changes slightly with temperature because liquids expand; molality (moles per kg of solvent) does not. If you only need moles from a mass, leave the volume at 1 L and read the moles line.
Worked example
Dissolving 5.844 g of sodium chloride (58.44 g/mol) gives 0.1 mol. Made up to 0.5 L, the solution is 0.2 M (200 mM). To make 0.5 L of 1 M NaCl you would need 1 × 0.5 × 58.44 = 29.22 g.
Frequently asked questions
What is the difference between molarity and molality?
Molarity is moles per liter of solution; molality is moles per kilogram of solvent.
How do I find molar mass?
Add the atomic masses of every atom in the formula. Water, H₂O, is 2 × 1.008 + 16.00 = 18.02 g/mol.
What does 1 M mean?
One mole of solute in one liter of solution.
How do I convert molarity to mg/mL?
Multiply molarity by molar mass to get g/L, which equals mg/mL.
Updated October 2026. Results are estimates for education, not financial or medical advice. All math runs in your browser; nothing you type is sent anywhere.