Durations

Duration is the amount of time that elapses between the start and end of an event or state. It is a scalar quantity representing how long something lasts, distinct from the specific clock time at which it begins or ends.

The standard International System of Units (SI) measures duration in seconds, with subdivisions such as milliseconds and microseconds. Durations are often expressed using designated formats, including ISO 8601 representations like PnDTnHnMnS for calendar durations.

In everyday use, durations describe the length of activities, such as a meeting, a commute, or a lecture. In media, duration refers to runtime for films or videos and to the relative lengths of notes and rests in music, where tempo influences perceived duration.

In computing and data processing, duration denotes elapsed time to complete a task, commonly reported as wall-clock time or CPU time. Time measurement can be affected by clock precision and system load.

In finance, duration is a measure of how responsive a fixed-income instrument’s price is to changes in interest rates, with concepts such as Macaulay duration and modified duration. In physics and biology, a particle’s lifetime or a radioactive half-life describes how long a state persists before decay.

Perceived duration varies with attention, arousal, and context, so psychological studies distinguish objective time from subjective duration. Overall, duration is a fundamental notion across disciplines for quantifying the length of time an event lasts.