Molarity Calculator (Solve for M, Moles, Volume or Mass)
Pick what you want to solve for, then enter the other values. The molar mass converts between grams and moles.
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Formula
M = n / Vwhere M is molarity (mol/L), n is moles of solute and V is the solution volume in litres.n = m / MMwhere m is the mass in grams and MM is the molar mass in g/mol.- Rearranged:
n = M × V,V = n / M,m = M × V × MM.
Worked example
Dissolve 5.844 g of NaCl (molar mass 58.44 g/mol) in enough water to make 100 mL of solution.
- Moles: 5.844 ÷ 58.44 = 0.1 mol
- Volume: 100 mL = 0.1 L
- Molarity: 0.1 ÷ 0.1 = 1 mol/L
To make 250 mL of 0.5 M NaCl instead: 0.5 × 0.25 L = 0.125 mol, and 0.125 × 58.44 = 7.305 g.
Frequently asked questions
How do I calculate molarity?
Divide moles of solute by litres of solution: M = n / V. If you only know the mass, first divide it by the molar mass. 5.844 g of NaCl (58.44 g/mol) is 0.1 mol, and in 0.1 L that is 1 mol/L.
How many grams do I need to make a solution of a given molarity?
Multiply molarity by volume in litres to get moles, then multiply by molar mass. For 250 mL of 0.5 M NaCl: 0.5 × 0.25 = 0.125 mol, and 0.125 × 58.44 = 7.305 g.
Is the volume the solvent volume or the solution volume?
It is the final solution volume. Dissolve the solute in some solvent, then top up to the volume mark, for example in a volumetric flask.
What is the difference between molarity and molality?
Molarity is moles per litre of solution and changes slightly with temperature because the volume does. Molality is moles per kilogram of solvent and does not change with temperature.