Calculate molarity, solution mass, and stock dilutions
This molarity calculator solves for concentration, solute mass, or final solution volume while converting between M, mM, µM, and nM; grams, milligrams, micrograms, and nanograms; and liters, milliliters, and microliters. Enter the molecular weight in g/mol and leave the variable you want to calculate blank.
The core relationship is mass = molarity × volume × molecular weight, with molarity expressed in mol/L, volume in liters, and molecular weight in g/mol. Rearranging that equation gives molarity = mass / (molecular weight × volume). The separate dilution calculator uses C₁V₁ = C₂V₂ to determine how much concentrated stock and diluent are needed.
Example: preparing a molar solution
To make 100 mL of a 100 mM solution of a compound with a molecular weight of 58.44 g/mol, the required mass is 0.1 mol/L × 0.1 L × 58.44 g/mol = 0.5844 g, or 584.4 mg. Dissolve the solute and bring the solution to the final volume rather than adding the final volume of solvent.
Use the molecular weight printed on the specific reagent container, including hydrate or salt form where applicable. For critical work, verify the result against the protocol and account for purity, assay, density, or activity corrections that this calculator does not model.
For a multi-step concentration series, use the serial dilution calculator and plate planner.
Molarity calculator FAQ
What is the formula for molarity from mass?
Molarity equals mass divided by molecular weight and solution volume: M = m / (MW × V). Use grams, g/mol, and liters to obtain mol/L.
How do I calculate a stock dilution?
Use C₁V₁ = C₂V₂. The stock volume is V₁ = C₂V₂ / C₁; the diluent volume is the desired final volume minus the stock volume.
Are molarity and molality the same?
No. Molarity is moles of solute per liter of final solution. Molality is moles of solute per kilogram of solvent and is not calculated by this tool.