Molarity in one formula
Molarity is M = moles ÷ volume (L). Moles come from mass: moles = mass ÷ molar mass. So the combined formula is M = mass ÷ (molar mass × volume in L) — enter any two of mass/moles/volume and the calculator fills the third.
Example: 5.84 g of NaCl (58.44 g/mol) in 0.25 L gives 5.84 ÷ 58.44 = 0.1 mol, and 0.1 ÷ 0.25 = 0.4 M.
Lab habits that save mistakes
- Always convert volume to litres — the #1 molarity error is plugging mL straight in. 250 mL is 0.25 L.
- H₂SO₄ is tricky: concentrated sulfuric acid is sold by weight percent and density; use the mass, not the bottle's "M" label, for dilutions.
- Hydrates: CuSO₄·5H₂O includes water in its molar mass (249.69 vs 159.61 for anhydrous) — weigh the hydrate, use the hydrate mass.
- Significant figures: molar mass values here are to 2 decimals; report answers to the precision of your least-precise input.
- For diluting stock solutions, see the Solution Dilution Calculator (C₁V₁ = C₂V₂).