Time zone abbreviations, and which ones clash

3 codes stand for two or more different offsets on this site.

IST is UTC+05:30 in India, UTC+02:00 in Israel, and UTC+01:00 in Ireland, where it is the summer time.

CST is UTC-06:00 in Chicago, UTC+08:00 in Shanghai and UTC-05:00 in Havana. Cuba's summer code, CDT, sits at UTC-04:00, an hour from the CDT of the central United States.

The time zone database lists IST for India, Ireland and Israel, and CST for both the central United States and China, as abbreviations in common English use. Ireland's is the odd one. Irish law makes the summer time the standard time, one hour ahead of Greenwich Mean Time, and calls the winter months Greenwich Mean Time, so the database records Ireland's IST as a summer code.

The time zone converter lists every place that uses a code you type, so you choose the one you mean.

Some governments use a code that clashes with a better-known one. This site keeps the database's letters, or shows none, and says why on the country's page.

Pakistan's metrology institute writes Pakistan Standard Time with the same three letters as the US Pacific zone. The site shows PKT, the database's code.

The Philippine Standard Time Act names its code PhST, with a small h. The database prints the Pacific letters for Manila, so the site shows the Act's code instead.

Bangladesh's time service writes the full name, Bangladesh Standard Time, and government pages shorten it to BST, the letters Britain uses for British Summer Time. The database prints a number for Dhaka, so this site shows the offset alone.

Saudi Arabia's standards body names the Saudi time standard and uses no code. The database prints a number for Riyadh too, so the site shows UTC+03:00. The letters some readers expect for Arabia belong to Atlantic time in the database.

Where the database prints only a number, this site adds a code only when a government, standards body or national time service uses it, and each one links its source below.

Added from official sources: SGT, MYT, NPT, LHST, LHDT and SLST. Replacing the database's letters by owner ruling, each explained on the page of the place that uses it: PCT, ABT, CDT and PhST. 1 code has no official source and is shown because readers know the place by it: GST.

Some database codes are also the official ones. The Hong Kong Observatory defines Hong Kong Standard Time, HKT, and Korea's national metrology institute keeps Korea Standard Time, KST.

142 zones print the offset and no code, following the database. Its rule is to use abbreviations in common English use, and numeric offsets where there are none, rather than letters it would have to make up.

Most of them still have an everyday name. 9 names are shared by several zones or countries and listed below. 77 names belong to one zone in one country, from Acre Time in Rio Branco to Yekaterinburg Time in Yekaterinburg. 50 zones have no name in the data, mostly in Russia, Jordan, Syria, Kazakhstan and Brazil. The time zone list links every one of them.

One row per code, 57 in all, with its meaning, its offset and the countries that use it. A code that clashes lists each meaning.