Molarity Calculator
0.0000 mol/L molarity
| Target Molarity | Volume of Stock Solution Needed |
|---|
How Molarity Is Calculated
Molarity (M) is defined as moles of solute per liter of solution: M = n ÷ V, where n is the number of moles and V is the solution volume in liters. Since most lab measurements start with a mass in grams rather than a mole count, this calculator first converts mass to moles using n = mass ÷ molar mass (molar mass in g/mol, found from a compound's formula and the periodic table), then divides by the solution volume you enter. Note that molarity is defined relative to the total volume of the final solution — not the volume of solvent added — which is why lab procedures for making a solution call for adding solute to some solvent and then adding solvent up to a calibrated final volume mark, rather than adding a fixed volume of solvent to the solute.
Dilution: C₁V₁ = C₂V₂
Once you know the molarity of a stock solution, the dilution equation C₁V₁ = C₂V₂ lets you find how much of that stock to use for a weaker target concentration, since the total moles of solute stay constant during dilution — only the volume changes. The reference table above uses your calculated molarity as C₁ and solves for V₁ against a few common target concentrations, assuming a final diluted volume equal to the solution volume you entered.
A Common Mixup: Molarity vs. Molality
Molarity (mol/L of solution) is volume-based and shifts slightly with temperature because liquids expand and contract, while molality (mol/kg of solvent) is mass-based and temperature-independent — that distinction matters in precise chemistry work but is usually negligible for typical lab or classroom dilutions. If you're converting between measurement systems for the inputs themselves, the conversion calculator and density calculator can help translate mass and volume units before you plug numbers in here.
Frequently Asked Questions
How do I calculate molarity from grams instead of moles?
First convert mass to moles by dividing the mass of solute (in grams) by its molar mass (in g/mol) — found from the compound's chemical formula. Then divide moles by the solution's total volume in liters to get molarity (M = n / V). This calculator does both steps automatically.
Does molarity depend on how much solvent I add?
No — molarity is defined relative to the final total volume of the solution, not the volume of solvent used to get there. That's why standard lab procedure is to dissolve the solute and then add solvent up to a calibrated final volume mark, rather than adding a fixed amount of solvent beforehand.