What is molarity?
Molarity (M) is the concentration of a solution expressed as moles of solute per liter of solution. It is one of the most common ways chemists describe how concentrated a solution is. This calculator finds molarity directly from the mass of solute you weigh out, its molar mass, and the final volume of solution.
How to use this calculator
Enter three values: the mass of solute in grams, the molar mass of the compound in grams per mole (g/mol), and the total volume of the solution in liters. The tool first converts mass to moles, then divides by volume to give molarity in mol/L. Make sure your volume is in liters — if you measured in milliliters, divide by 1000 first.
The formula explained
The calculation has two steps. First, moles of solute equal mass divided by molar mass: \(n = m / MW\). Second, molarity equals moles divided by volume in liters: \(M = n / V\). Combined, this gives $$M = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)} \times \text{Volume (L)}}$$ Molar mass comes from the periodic table — for example, sodium chloride (NaCl) is about 58.44 g/mol.
Worked example
Suppose you dissolve 58.44 g of NaCl (molar mass 58.44 g/mol) into water to make 2 liters of solution. Moles \(= 58.44 / 58.44 = 1\) mol. Molarity $$M = \frac{1\ \text{mol}}{2\ \text{L}} = 0.5\ \text{M}$$ So the solution is 0.5 molar.
FAQ
What if my volume is in milliliters? Convert to liters by dividing by 1000 before entering it (e.g. 250 mL = 0.25 L).
Is volume the solute volume or total solution volume? Always use the total final volume of the solution, not just the solvent.
How do I find molar mass? Add the atomic masses of all atoms in the formula using the periodic table, or look it up for the compound.
