What is GMT? Difference Between GMT and UTC.

GMT Full Form

Mahesh Sharma
3 min readNov 26, 2023

GMT, which stands for Greenwich Mean Time, is a term commonly used in the field of timekeeping and global time standards. GMT is the primary time standard by which all other time zones are referenced. It is also known as Zulu time or Coordinated Universal Time (UTC).

What is GMT? Difference Between GMT and UTC

GMT Introduction

GMT is calculated based on the position of the Sun relative to the Prime Meridian, an imaginary line running from the North Pole to the South Pole and passing through Greenwich, England. Greenwich Mean Time is the average time it takes for the Sun to cross the Prime Meridian at solar noon (12 p.m.).

The concept of GMT was first proposed in 1884 at the International Meridian Conference, held in Washington D.C. The conference was attended by representatives from 25 countries, who agreed to establish a universal time standard in order to facilitate international communication and transportation.

To determine the current GMT time, it is necessary to know the difference between the local time and GMT in your location. For example, if you are in the eastern time zone of the United States, you would need to subtract 5 hours from the local time to get the current GMT time.

Although GMT is still used as a reference for time zones around the world, it has been largely replaced by Coordinated Universal Time (UTC) as the global standard for timekeeping. UTC uses atomic clocks to track time with greater accuracy than GMT, which relies on the Earth’s rotation. However, GMT remains an important historical reference for global time standards.

Difference Between GMT and UTC

GMT and UTC are two different but closely related time standards used for timekeeping around the world. Here are some key differences between the two:

Definition: GMT is determined by the mean solar time at the Prime Meridian, which is located in Greenwich, England. UTC, on the other hand, is a time standard that is based on the International System of Units (SI) and uses atomic clocks to measure time.

Accuracy: Because GMT is based on the Earth’s rotation, it can be affected by factors such as the Earth’s irregular rotation, tides, and atmospheric conditions. This can make GMT less accurate than UTC, which uses atomic clocks. UTC is therefore considered a more precise timing standard.

Leap seconds: Another difference between GMT and UTC is how they handle leap seconds. A leap second is an adjustment that is made to atomic clocks to keep them in sync with the Earth’s rotational rate. GMT does not have leap seconds, whereas UTC does. This means that occasionally UTC time will differ by one second from atomic time, because of the inclusion of the leap second.

Naming conventions: Although GMT is still used widely, it has been largely replaced by UTC as the global time standard. UTC is sometimes referred to as Universal Time (UT), Coordinated Universal Time (CUT), or, less commonly, Greenwich Mean Time (GMT).

GMT and UTC are two different time standards that have different origins, methods of measurement, precision and handling of leap seconds. Greenwich Mean Time (GMT) is the original basis for standard times throughout the world but is now mostly replaced by Coordinated Universal Time (UTC) as an accurate reference time standard.

In conclusion, the full form of GMT is Greenwich Mean Time. It is a global time standard used as a reference for time zones around the world. GMT was established in 1884 at the International Meridian Conference, and although it has largely been replaced by Coordinated Universal Time (UTC), it remains a significant historical reference for timekeeping.

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Mahesh Sharma

Hey, I'm Mahesh Sharma, a passionate digital marketer with 10+ years of experience in the field. I'll be sharing topics such as SEO, SMO, PPC/ SEM.