⚗️Molarity Calculator

About this tool

Choose what to solve for: the mass to weigh, the molarity or the volume. Pick a common compound such as sodium chloride, Tris or glucose, or type any molar mass. Enter the other values with units from molar to nanomolar and from litres to microlitres. The result includes the number of moles and a plain instruction for making up the solution.

How to calculate molarity

Molarity, written M or mol/L, is the number of moles of solute per litre of solution. The mass you need is molarity × volume in litres × molar mass. To make 250 mL of 0.5 M sodium chloride, with a molar mass of 58.44 g/mol, you need 0.5 × 0.25 × 58.44 = 7.305 g. Working the other way, dissolving 7.305 g of NaCl to make 250 mL gives 7.305 ÷ 58.44 ÷ 0.25 = 0.5 M. Always use the molar mass of the exact form on the bottle: copper sulfate pentahydrate (CuSO₄·5H₂O) is 249.69 g/mol, much more than anhydrous CuSO₄ at 159.61. The volume is the final volume of solution, not the volume of water added. Dissolve the solid in less solvent than needed, then top up to the mark in a volumetric flask. Honest limits: concentrated liquids such as acids are normally measured by volume using their density and percentage strength, and this calculator doesn't handle that. Always follow your lab's safety rules, including adding acid to water, never the reverse. The molar mass calculator finds molar masses from formulas, the dilution calculator makes weaker solutions from a stock and the pH calculator works out acidity.

Frequently asked questions