What is Greenwich Mean Time (GMT)?

GMT stands for Greenwich Mean Time. It is the yearly average of the time each day when the Sun crosses the Prime Meridian at the Royal Observatory in Greenwich, London.

Quick Answer

GMT stands for Greenwich Mean Time. It's the time zone based on the Prime Meridian in Greenwich, London. While it was once the world's primary time standard, it has largely been replaced by the more precise Coordinated Universal Time, or UTC. For everyday purposes, GMT and UTC are often considered the same.

The Definition of GMT

GMT stands for Greenwich Mean Time. It is a time zone that is based on the solar time at the Royal Observatory in Greenwich, London, which is located on the Prime Meridian (0° longitude).

Key Facts About GMT:

  • Historical Standard: GMT was originally used as the world's time standard, from which all other time zones were referenced.
  • Location: It is the local time in the United Kingdom during the winter months (from late October to late March).
  • GMT vs. UTC: In modern usage, GMT is often used interchangeably with Coordinated Universal Time (UTC). While practically the same for most purposes, UTC is a more precise atomic time standard, whereas GMT is based on the Earth's rotation.

Conclusion

GMT stands for Greenwich Mean Time and serves as the baseline time zone (UTC+0). While it is technically a time zone, it is often used as a synonym for UTC, the modern world's time standard. Explore different time zones on our Time Zone Map.