Days (d)
A day is a unit of time defined as exactly 86,400 seconds, representing the average duration of one rotation of the Earth relative to the Sun. This definition is fixed by the International System of Units (SI) and used for civil timekeeping worldwide [bipm-si-brochure].
Origin
The day has been used as a time unit since antiquity, based on the Earth’s rotation. The modern definition was standardized by the General Conference on Weights and Measures (CGPM) to align with atomic time in 1967 [cgpm-resolutions].
Worldwide Use
Days are the universal standard for time measurement in calendars, science, and daily life worldwide. They serve as the base unit for longer time periods such as weeks, months, and years [bipm-si-brochure].
Common References
- One day equals 24 hours or 86,400 seconds
- Used to schedule work, sleep, and daily activities
- Basis for calendars and time zones globally