Molarity Calculator
Calculate molarity from solute mass, molecular weight and final volume, or calculate required mass for a target molarity.
Calculate molarity or required solute mass
Convert between mass, formula weight, solution volume and molar concentration.
How the Molarity Calculator works
Molarity is moles of solute per litre of final solution. Moles equal mass ÷ formula weight, so M = mass/(formula weight × litres). Rearranging gives mass = molarity × litres × formula weight, the same relationship shown in Sigma-Aldrich laboratory calculation guidance.
How to use this molarity calculator
Choose whether to solve for molarity or required mass. Enter the exact formula weight for the reagent form you are using, including hydrate or salt form where relevant, and the final prepared solution volume. When making a solution, dissolve the reagent and bring the solution to final volume rather than simply adding that volume of solvent.
How to interpret the result
The tool reports molarity in mol/L and mM plus moles of solute, which makes unit checks easier. If the formula weight is wrong, every concentration result will be wrong by the same proportional factor, so verify the bottle label, certificate of analysis or validated reagent specification.
Assumptions and limitations
Molarity is temperature-dependent through solution volume and does not directly describe activity, normality, osmolality or mass fraction. Purity and assay may require a correction not included here. Concentrated commercial acids/bases often need density and weight-percent calculations rather than a simple solid-mass formula.
Practical example and workflow
For 5.844 g NaCl (formula weight about 58.44 g/mol) brought to 1 litre final volume, the calculation gives 0.1 mol/L or 100 mM. Reversing the mode shows the same 5.844 g mass required for a 0.1 M, 1 L solution.