Concentration Converter

ppm, ppb, mg/L, and mass percent for dilute aqueous solutions (ρ ≈ 1 kg/L).

Internally your entry becomes a bare mass fraction, and the four columns are that fraction wearing different exponents — a million for parts per million, a billion for parts per billion, a hundred for mass percent. Fifty ppm therefore resolves to 50,000 ppb and 0.005 percent, and the arithmetic between those three is exact. The column carrying an assumption is mg/L. Parts per million is a ratio of masses, milligrams of solute in a kilogram of solution, while milligrams per litre is a mass in a volume, and the two only coincide when a litre of the solution happens to weigh a kilogram. Dilute water near room temperature obliges, which is why drinking-water and wastewater reports use the two interchangeably, and the engine states the assumption in its own note rather than hiding it. It breaks down for seawater at roughly 1.025 kg/L, worse for brines and concentrated acids, and badly for organic solvents where a litre may weigh 700 grams or 1.5 kilograms. Nothing molar is available: with no molar-mass field the page cannot reach mol/L, molality or normality, so a chemist working from a formula weight has to take that step separately. Gas-phase ppmv is out of reach for the same structural reason, being a volume ratio that needs both temperature and pressure to pin down. Mass percent is carried to nine decimals so that single-digit ppb entries do not round away to nothing.