Molarity Calculator
Calculate solution molarity from moles and volume, or mass and molecular weight. Get accurate results with charts and breakdowns for chemistry and lab work.
About This Calculator
The Molarity Calculator is a free online tool for chemistry students, researchers, and laboratory professionals who need to calculate the concentration of a solution. Molarity (M) is one of the most important concepts in chemistry, representing the number of moles of solute per liter of solution.
The calculator supports two methods for determining molarity. In the Moles & Volume method, simply enter the number of moles of solute and the solution volume in liters to get the molarity using the formula M = n / V. In the Mass & Molecular Weight method, enter the mass of solute in grams and its molecular weight in g/mol to first calculate the number of moles (n = mass / molecular weight), then the calculator computes the molarity using the same formula. This is particularly useful when preparing solutions from solid reagents.
Molarity is used across all branches of chemistry — from preparing buffer solutions in biology labs to determining reaction stoichiometry, calculating dilution factors, and performing titrations. Accurate molarity calculations are essential for reproducible experimental results, quality control in pharmaceutical manufacturing, and ensuring correct dosage in clinical chemistry.
Formula
Molarity (M) = Number of Moles of Solute (n) / Volume of Solution (V) in liters
When using mass: n = Mass of Solute (g) / Molecular Weight (g/mol)
Regional Notes
This calculator uses SI units (moles, liters, grams) which are the international standard for chemistry and are used universally in IN, US, and UK laboratories. Molecular weights are expressed in g/mol and should be calculated from the periodic table based on the atomic masses of the elements in the compound.
Frequently Asked Questions
How does the Molarity Calculator work?
The calculator uses the formula M = n / V where M is molarity, n is the number of moles of solute, and V is the volume of solution in liters. You can either enter moles and volume directly, or provide the mass and molecular weight of the solute to calculate moles first (n = mass / molecular weight).
What is molarity?
Molarity (M) is the number of moles of solute dissolved per liter of solution, expressed in mol/L. It is the most common way to express concentration in chemistry and is widely used in laboratories for preparing solutions and performing chemical reactions.
What is the difference between molarity and molality?
Molarity (M) is moles of solute per liter of solution, while molality (m) is moles of solute per kilogram of solvent. Molarity depends on temperature because volume changes with temperature, whereas molality is temperature-independent since it uses mass of solvent.
How do I make a 1 M solution?
To make a 1 M solution, weigh out the molecular weight of the substance in grams (its molar mass), dissolve it in less than 1 liter of solvent, and then add enough solvent to bring the total volume to exactly 1 liter. For example, to make 1 M NaCl, dissolve 58.44 g of NaCl in water and dilute to 1 L.
How do I convert mass concentration to molarity?
To convert mass concentration (g/L) to molarity, divide the mass concentration by the molecular weight of the substance: M = concentration / molecular weight. For example, a 10 g/L solution of NaCl (MW = 58.44 g/mol) has a molarity of 10 / 58.44 = 0.171 M.
What is the molarity of water?
Pure water has a molarity of approximately 55.5 M at 25°C. This is calculated by dividing the density of water (1000 g/L) by its molecular weight (18.015 g/mol): 1000 / 18.015 = 55.5 mol/L.
How do I calculate pH from molarity?
For strong acids, pH = -log[H+], where [H+] is the molarity of the acid. For example, a 0.01 M HCl solution has pH = -log(0.01) = 2. For strong bases, first find pOH = -log[OH-], then pH = 14 - pOH. This applies only to strong acids and bases that fully dissociate.
What units can molarity be expressed in?
Molarity is most commonly expressed in moles per liter (mol/L) or molar (M). It can also be expressed as moles per cubic decimeter (mol/dm³), which is equivalent to mol/L. In some contexts, millimolar (mM, 10⁻³ M) or micromolar (µM, 10⁻⁶ M) are used for dilute solutions.