Donaldson R F PPM & PPB Converter
Convert concentrations between ppm, ppb and percentage, or work one out from a mass ratio.
How this is worked out
Parts per million and parts per billion are just very small percentages, scaled to be easier to read: 1 ppm = 1 part in 1,000,000 = 0.0001%, and 1 ppb = 1 part in 1,000,000,000 = 0.0000001%. They're ratios, so any pair of matching mass units works (both in grams, both in kilograms, and so on) — the units cancel out, leaving a pure number. For a dilute water-based solution, 1 mg of solute per litre of solution is commonly treated as approximately 1 ppm, because a litre of water weighs almost exactly 1 kg (this approximation gets worse for denser solutions or solvents other than water).
Frequently asked questions
Is ppm always a mass ratio?
Not necessarily — it can also be a volume ratio (common for gas concentrations, like CO₂ in air) or a mole ratio; this tool works in mass ratios, the most common convention for concentrations in solution.
Why use ppm instead of a percentage?
Writing "2 ppm" is easier to read and compare than "0.0002%" — once a concentration is far below 1%, the extra decimal places in a percentage stop being useful, and ppm (or ppb, for even smaller amounts) keeps the numbers in an easy, whole-number range.
Related tools: Dilution Calculator, Molarity & Molality Calculator, Molar Mass Calculator.
Source / Last verified: standard definitions of parts-per-million/billion as mass ratios (general/analytical chemistry) — read/checked 1 October 2026.