🧫 Molarity Calculator

How to Use This Calculator

Select the variable you want to calculate, enter the two known values, and click Calculate. The tool solves M = n/V for molarity, or rearranges to find moles or volume depending on your selection.

Molarity Formula

Molarity (M) is the number of moles of solute (n) divided by the volume of solution (V) in litres. To prepare a 0.1 M solution of NaCl in 500 mL, you calculate n = 0.1 × 0.5 = 0.05 mol, then weigh out 0.05 × 58.44 = 2.92 g of NaCl and dissolve it in water, adding water until the total solution volume reaches exactly 500 mL in a volumetric flask. Volume is always the total solution volume, not just the volume of water added.

Worked Examples

Where This Calculation Comes Up

Molarity is the most commonly used concentration unit in lab work. Every time you prepare a stock solution, a buffer, a titrant, or a reagent solution, you calculate the mass of solute using molarity. If a procedure says "add 10 mL of 0.1 M HCl," you are using molarity to determine that those 10 mL contain 0.001 mol of HCl. Titration calculations depend entirely on molarity: at the equivalence point, the moles of acid equal the moles of base, and those moles come from M × V for each solution.

In clinical labs, blood tests report analyte concentrations in millimolar (mM) or micromolar units, but the underlying calculation is the same M = n/V. A blood glucose level of 5 mM means 5 × 10⁻³ mol per litre of blood. Pharmacology uses molarity to calculate drug concentrations in solutions, and cell biology uses it to prepare growth media. The dilution formula C₁V₁ = C₂V₂, used every time you dilute a concentrated stock, is simply molarity applied twice. Understanding M = n/V is the foundation for all of these calculations.