onebillionth

One billionth is the fraction 1/1,000,000,000, equal to 10^-9. In scientific and most modern usage, this value represents one unit divided into a billion equal parts.

In the International System of Units (SI), 10^-9 is the basis for the nano- prefix, giving units such as nanometer (nm), nanosecond (ns), and nanogram (ng). These denote one billionth of a meter, second, or gram, respectively. Notation can be written as 1×10^-9 or 0.000000001.

Applications and examples of one billionth appear across science and engineering. It is central to nanoscale measurements and technologies, such as semiconductor fabrication, molecular biology, and materials science. In probability and statistics, a one in a billion event has a probability of 10^-9. In practice, timing and performance are often discussed in nanoseconds, while data storage and signal processing may reference nanometer-scale dimensions or nano-second intervals.

History and terminology note that the word billion has undergone regional variation in the past, which could affect meaning outside scientific contexts. In contemporary scientific usage, however, a billionth corresponds to 10^-9, and the SI nano- prefix formalizes this scale across units. This standardization supports consistent communication in science, engineering, and related fields.