Time in Thailand
Thailand follows UTC+7, which is seven 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 it changed to Indochina Time, GMT+07:00.
- Prior to 1 January 1901 locations in Siam with an astronomical observatory would adopt local mean time based on the observatory's geographic position. Chiang Mai Province and two other provinces each had an observatory, hence, each province had its own distinct local mean time, with minutes of difference between the three locations.
- 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 at the 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+06:42:04||Bangkok Mean Time|
|1 April 1920 – present||UTC+07:00||Indochina Time (ICT)|
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).