![cover image](https://wikiwandv2-19431.kxcdn.com/_next/image?url=https://upload.wikimedia.org/wikipedia/commons/thumb/8/8f/Fluorescein_%25282%2529.jpg/640px-Fluorescein_%25282%2529.jpg&w=640&q=50)
Parts-per notation
Set of units to describe small values / From Wikipedia, the free encyclopedia
"Parts per billion" redirects here. For the film, see Parts per Billion.
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement. Commonly used are parts-per-million (ppm, 10−6), parts-per-billion (ppb, 10−9), parts-per-trillion (ppt, 10−12) and parts-per-quadrillion (ppq, 10−15). This notation is not part of the International System of Units (SI) system and its meaning is ambiguous.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/8/8f/Fluorescein_%282%29.jpg/640px-Fluorescein_%282%29.jpg)