Difference Between GMT and IST - Fullform, Current IST Time & More

Greenwich Mean Time (GMT) and Indian Standard Time (IST) are two widely used time standards, primarily used to determine the time in various parts of the world. GMT denotes the time on the Prime Meridians (longitude 0 degrees) and is a basis for worldwide timekeeping. IST, however, is the time zone utilized by India, which is GMT plus 5 hours and 30 minutes. In other words, 5 hours and 30 minutes form the difference between GMT and IST. For this reason, when GMT shows 12:00 noon, IST would be 5:30 PM.

The topic Difference Between IST and GMT, falls under Geography, General Studies Paper I of the UPSC Civil Services Examination. Understanding global time zones, longitude, and latitude plays a critical role in answering questions related to world geography, international relations, and the global positioning system.

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What is the difference between GMT and IST?

Here is a table comparing Greenwich Mean Time (GMT) and Indian Standard Time (IST):

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GMT to IST Calculator

IST to GMT Calculator

Greenwich Mean Time (GMT) is the time zone based on the mean solar time at the Royal Observatory in Greenwich, London, UK. It is the standard time used in the UK during the winter months and the reference time for many other time zones worldwide. GMT is defined as the time at the Prime Meridian, which is the imaginary line that runs from the North Pole to the South Pole and passes through the Royal Observatory in Greenwich. The Prime Meridian is used as the basis for measuring longitude and is defined as 0 degrees longitude.

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What is IST (Indian Standard Time)?

Indian Standard Time (IST) is the time zone used in India, which is 5 hours and 30 minutes ahead of Coordinated Universal Time (UTC+5:30). IST is used throughout India, including major cities such as New Delhi, Mumbai, Kolkata, and Chennai. IST was established in 1947, following India's independence from British colonial rule. It replaced the previous time zone used in India, based on the local mean time of 82.5° E longitude. IST is used as the standard time in India for all official purposes, including railway and airline schedules, and is observed throughout the country. It is also the basis for the time used in neighboring countries such as Sri Lanka and Bangladesh.

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Key Facts About the Indian Standard Time

The Council of Scientific & Industrial Research – National Physical Laboratory (CSIR-NPL), which maintains the Indian Standard time, has proposed the need for two time zones in India – 

• IST I (UTC+5:30) for the entire country and
• IST II (UTC+6:30) for the North-Eastern region of the country. 

This is because the early sunrise in the easternmost parts of the country due to the longitudinal extent of the country causes the loss of many daylight hours there. However, the Government of India has not favored the proposal for two time zones due to its difficulties and complexities.

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