Molarity Calculator

Molarity measures solution concentration as moles of solute per liter of solution (M = n/V). The Molarity Calculator solves for molarity, moles of solute, or volume of solution when you know the other two, supporting multiple unit systems for amount (mol, mmol), volume (L, mL), and concentration (M, mM). It can also calculate mass when you provide the molar mass.

Students prepare laboratory solutions, chemists calculate reagent quantities for reactions, and pharmaceutical technicians compound medications. The calculator handles unit conversions automatically and displays results in multiple units for flexibility in lab settings.

Because calculations run entirely in your browser using JavaScript, you can solve solution concentration problems without any data leaving your device. The tool clearly distinguishes between molarity and molality in the FAQ section, a common point of confusion.

Molarity is the number of moles of solute divided by the volume of solution in litres, and the tool rearranges that to solve for whichever of the three you are missing. Concentration expressed this way is the working currency of solution chemistry because it counts particles rather than mass, and reactions proceed on particle counts.

The distinction that catches people out is that the volume is of the finished solution, not of the solvent added. Dissolving a solid changes the total volume, so proper preparation means adding solvent up to a calibrated mark in a volumetric flask rather than measuring out a litre of water and stirring the solute into it.

An optional molar mass field lets you work from grams instead of moles, since a balance weighs mass while the equation wants moles. Dividing the mass by the molar mass bridges the two.

Molarity is not the only way to express concentration and is not always the right one. Molality — moles per kilogram of solvent — is preferred where temperature varies, because it depends on mass rather than volume and mass does not expand when warmed. Normality accounts for the number of reactive equivalents and matters for acid-base and redox work, where a diprotic acid supplies two protons per molecule. Percentage by mass or volume is common in commercial preparations.

Because it is defined per litre, a molar concentration changes with temperature even though no material has been added or removed: warm a solution and it expands, so the same moles occupy more volume and the molarity falls slightly. For precise work, prepare and use solutions at a stated temperature.

For dilutions, the relationship you want is that moles are conserved — the initial concentration times initial volume equals the final concentration times final volume. And always add concentrated acid to water rather than the reverse, since the reaction is strongly exothermic; laboratory work needs appropriate protection and supervision.