Concentration Converter (ppm, Molarity, %)

Saline, % w/v to millimolar. 0.9 % w/v means 0.9 g per 100 mL, which is 9 g per litre. 9 g ÷ 58.44 g/mol = 0.1540 mol, so normal saline is 0.1540 M = 154.0 mM. No density is needed, because both units are per volume of solution.

Concentrated sulfuric acid, % w/w to molarity. One litre weighs 1,000 mL × 1.84 g/mL = 1,840 g, of which 98 % is acid: 1,803.2 g. 1,803.2 ÷ 98.072 = 18.39 M, and with two H⁺ per molecule, 36.77 N. Only 1,840 − 1,803.2 = 36.8 g of the litre is water, so the molality is a startling 499.6 mol/kg.

The common mistake: reading % w/w as if it were % w/v. Treating 98 % H₂SO₄ as 98 g per 100 mL gives 980 g/L ÷ 98.072 = 9.993 M, barely half the true 18.39 M, because it ignores that a litre of the acid weighs 1.84 kg. Mass-based units (% w/w, ppm, molality) only become per-litre units through the density.

Each unit grew up in a trade that needed it. Analysts weighing precipitates think in mass per mass, so assay certificates and food labels give % w/w and environmental limits give ppm or ppb. Pharmacists and clinicians measure liquids, so drips and eye drops are labelled % w/v (grams per 100 mL). Distillers measure volumes of alcohol: Joseph Gay-Lussac’s alcoholometer of 1824 made “degrees Gay-Lussac”, percent by volume, the standard for spirits, which is still how strength is printed on a bottle.

Chemists count particles. Jeremias Richter coined the word stoichiometry in 1792 and tabulated equivalent weights, the amounts of acids and bases that exactly neutralise each other, which is where normality comes from. Once Wilhelm Ostwald popularised the mole in the 1890s, moles per litre (molarity) became the bench unit, and moles per kilogram of solvent (molality) became the unit of physical chemistry, because it does not change when a liquid expands with temperature and it is what freezing-point and boiling-point laws use.

IUPAC now calls molarity “amount concentration” and discourages normality, since the number of equivalents depends on the reaction: H₃PO₄ can give 1, 2 or 3. Water-quality reports keep it in the form of meq/L. Molar masses here use the IUPAC conventional atomic weights, the same as the Molar Mass Calculator.

This converter takes a concentration in any common unit and gives it in all the others. It works through one litre of solution: the density gives the litre’s mass, the starting unit gives the grams or moles of solute in it, and the solvent is what is left. From that litre every unit follows by definition, so the conversions agree with each other exactly.

It says when an answer depends on the density, and when a unit cannot be reached without a molar mass or a pure-solute density. The drawing splits the litre into solute and solvent by mass and by moles, and Show Work lists every step for the pair you chose. Everything runs in your browser.

It is meant for students, lab staff reading reagent labels, and anyone turning a water report’s mg/L into molarity or ppm.

Related tools: Molarity Calculator, Dilution Calculator, and Empirical & Molecular Formula Calculator.