GMT(Greenwich Mean Time)
Greenwich Mean Time (GMT) is mean solar time at the Greenwich meridian, and in civil use it is the same clock reading as UTC.
- UTC offset
- UTC±00:00
- Abbreviation
- GMT
- Full name
- Greenwich Mean Time
- Military letter
- Zulu (Z)
- Regions
- United Kingdom, Ireland, Iceland, West Africa
- IANA zones
- Europe/London, Atlantic/Reykjavik, Africa/Accra, Africa/Abidjan
- Converter model
- Fixed offset.
What GMT means
GMT is the winter civil time of the United Kingdom and Ireland and is kept year-round by several West African countries; it is also still used as a general label for the zero offset.
- For civil purposes GMT and UTC show the same time; they differ in how they are defined, not in what a clock reads.
- GMT is astronomical in origin, while UTC is generated from atomic clocks — which is why technical standards prefer UTC.
Cities on this offset
These cities keep UTC±00:00 as their standard offset:
- London
- Dublin
- Reykjavík
- Accra
- Abidjan
Zones with the same offset
- UTC — Coordinated Universal Time (UTC±00:00)
History
Greenwich Mean Time grew out of the Royal Observatory's work on navigation and was adopted as the world's prime meridian at the International Meridian Conference in 1884, making it the basis of global timekeeping until UTC took over that role.
Do not confuse with
- UTC — Coordinated Universal Time
- WET — Western European Time