Greenwich Mean Time (GMT)

The "Greenwich Mean Time" refers to the time zone at the zero degree of longitude that runs through the London suburb of Greenwich, from which it takes its name. It is also called the zero meridian.

In summer, Great Britain and the Channel Islands change their clocks to British Summertime (BST). Ireland refers to its summer time as Irish Summertime. Even then, the time difference to our summer time (CEST) is -1 hour. African countries, on the other hand, have no daylight saving time.

Greenwich Mean Time is officially valid in 22 countries.

Current British Summertime:
Wednesday, May 24, 2023

GMT and UTC - Coordinated World Time

The differences between the individual time zones are always given in relation to the "Universal Time Coordinated" (UTC), i.e., the time that exists on the zero meridian (zero longitude). Most parts of Central Europe are in the UTC +1 time zone. For Greenwich Mean Time, the time zone UTC +0 applies.

The Greenwich Mean Time corresponds to the UTC 0 time zone, i.e., the Coordinated World Time with an offset of 0 hours. It corresponds to Western European time, which is valid in Portugal, for example, but is officially referred to as GMT in the United Kingdom and several African countries. The different designation of the same time zone often leads to confusion. GMT is the name of the time zone, while UTC is a term for a time system that also has its normal state on the zero meridian.

Countries in Greenwich Mean Time

GMT time applies to the following countries:

Burkina FasocountrywideGMTnone
Isle of MancountrywideGMTBST
Ivory CoastcountrywideGMTnone
Saint Helena, Ascension and Tristan da CunhacountrywideGMTnone
Sao Tome and PrincipecountrywideGMTnone
Sierra LeonecountrywideGMTnone
United KingdomcountrywideGMTBST

Origin of the Greenwich Mean Time

During seafaring times, there were different zero meridians and systems for position calculation depending on the nation. One of the best known was already based on the Greenwich meridian. It was not until 1884 that a globally uniform time system was agreed upon, dividing the globe into 24 equal-sized areas according to their longitudes. Each section of 15° corresponded to one hour, which, at least in theory, resulted in 24 uniform time zones. When the date line was established in a preferably uninhabited area between Asia and America, the zero meridian was established on the opposite side of the globe in Greenwich. Only with this worldwide uniform regulation did the coordinates we know today exist. Previously, numerous coordinate systems competed with each other.

In the courtyard of the historic Royal Greenwich Observatory, a brass strip and a laser beam symbolize the zero meridian. The geographically correct position is about 100 meters further east.

Further Countries in the same timezone of UTC +0

Although the timezone is named "Greenwich Mean Time", it is mostly for politcal reasons. It simply means that, e.g., the beginning and ending of daylight savings time always apply here uniformly. There are some other countries, in which the clock strikes the same hour. These countries have the same temporal distance to UTC (Universal Time Coordinated):


The time zones and times listed here are based on the IANA "Olsen" time zone database. Designations and their translations were adapted separately. Version used and update: Version 2022.4 on 11/27/2022.
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