Molarity formulas
Molarity (M) = moles ÷ liters of solution
Moles = mass (g) ÷ molar mass (g/mol)
Mass (g) = M × V (L) × molar mass
How to make a solution in the lab
- Use the calculator to find the mass of solute you need.
- Weigh it out and dissolve it in about three quarters of the final volume of solvent.
- Transfer to a volumetric flask and add solvent up to the line.
- Cap and invert several times to mix evenly.
Always follow your lab's safety rules. Acids and bases such as HCl, H₂SO₄ and NaOH need gloves and eye protection, and acid is added to water, never the other way around.
Example
How many grams of glucose make 250 mL of a 0.1 M solution? 0.1 mol/L × 0.25 L × 180.16 g/mol = 4.504 g.
Diluting a stock solution instead? Use the dilution calculator.
Last reviewed October 2026.
Frequently asked questions
What is molarity?
Molarity (M) is the concentration of a solution in moles of solute per liter of solution. A 1 M sodium chloride solution has 1 mole (58.44 g) of NaCl dissolved in enough water to make 1 liter in total.
How do I calculate the mass needed for a solution?
Mass (g) = molarity (mol/L) × volume (L) × molar mass (g/mol). To make 500 mL of 0.2 M NaCl: 0.2 × 0.5 × 58.44 = 5.844 g.
Is the volume the water or the final solution?
Molarity uses the final volume of the whole solution, not the volume of water added. In the lab, dissolve the solid in less water than you need, then top up to the mark in a volumetric flask.
What is the difference between molarity and molality?
Molarity is moles per liter of solution. Molality is moles per kilogram of solvent. Molality does not change with temperature, while molarity can, because liquids expand when warmed.
Where do I find the molar mass?
Add up the atomic masses of every atom in the formula from the periodic table. For water, H₂O: 2 × 1.008 + 16.00 = 18.02 g/mol. Common compounds are in the dropdown.