About Parts Per Notation

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.

Common parts-per notations in science and engineering include:

• ppm (parts per million): 10⁻⁶
• ppb (parts per billion): 10⁻⁹
• ppt (parts per trillion): 10⁻¹²
• ppq (parts per quadrillion): 10⁻¹⁵
• Percentage (%): 10⁻²
• Per-mil (‰): 10⁻³
• Per-myriad (‱): 10⁻⁴

Conversion Formulas