Time in Thailand
Thailand follows UTC+7, which is 7 hours ahead of Greenwich Mean Time and Coordinated Universal Time. The local mean time in Bangkok was originally GMT+06:42:04. Thailand used this local mean time until 1920, when they changed to Indochina Time GMT+07:00.
- Prior to 1 January 1901 - locations in Siam with an Astronomical Observatory would adopt the local mean time based on the Observatory's geographical position. Phayap and Ratchaburi all had their own observatories; hence, the three provinces had their respective Local Mean Time, with minutes of differences amongst the three locations.
- 1920 - On 1 April 1920 the mean time of the 105th meridian was adopted by Siam as the new Standard Time. The mean time of the 105th meridian is UTC+07:00 hours ahead of Greenwich Mean Time (i.e. Local Mean Time over Greenwich Royal Observatory near London, United Kingdom).
|Period in use||Time offset from GMT||Name of Time (unofficial)|
|1 January 1880 - 31 March 1920||UTC+6:42:04||Bangkok Mean Time|
|1 April 1920 – present||UTC+7||Indochina time|
Standardisation of time in Thailand
Thailand declared that people would move their clocks ahead by 17-minutes 56-seconds to match the time in use in Southeast Asia (UTC+06:42:04 hrs and UTC+07:00:00 ahead of Greenwich Mean Time) on 31 March 1920. The time was switched on 1 April 1920 at 06:00 (old time) to 06:17:56 (new time).