Parts-per notation

In <a href="/facts/Science/IJoaD7rs">science</a> and <a href="/facts/Engineering/RFVg8H3I">engineering</a> parts-per notation is set of pseudo-units to describe the small values of miscellaneous <a href="/facts/Dimensionless_quantity/TINrpQIq">dimensionless quantities</a>, e.g. <a href="/facts/Mole_fraction/nW4EepmJ">mole fraction</a> or <a href="/facts/Mass_fraction_(chemistry)/YMIH9egn">mass fraction</a>. 
Since these <a href="/facts/Fraction_(mathematics)/ghnQE9B3">fractions</a> are quantity-per-quantity measures, they are pure numbers with no associated <a href="/facts/Units_of_measurement/pvTpWbmC">units of measurement</a>. Commonly used are

<ul><li>parts-per-million - ppm, 10−6</li>
<li>parts-per-billion - ppb, 10−9</li>
<li>parts-per-trillion - ppt, 10−12</li>
<li>parts-per-quadrillion - ppq, 10−15</li></ul>
This notation is not part of the <a href="/facts/International_System_of_Units/S7YLglNz">International System of Units</a> - SI system and its meaning is ambiguous.

Parts-per notation open-in-new

Parts-per notation