Start with the station where you are and the station where you need to go. Use the official maps. Check each change, fare, ticket and last train for that trip.
Changing between BTS and MRT does not necessarily mean one fare or one ticket. Check the fare and ticket rules for each system used by the journey.
BTS and MRT are often described in a simple way. BTS is said to be above ground, while MRT is called the subway. That rule is no longer correct. The better difference is about the network and the bodies behind it.
The Thai and English name of BTS is รถไฟฟ้าบีทีเอส / BTS Skytrain. Bangkok Mass Transit System Public Company Limited, or BTSC, built and operates the system. BTS began service on 5 December 1999. Its two main routes are the สายสุขุมวิท / Sukhumvit Line and สายสีลม / Silom Line.
The first Sukhumvit section ran from Mo Chit to On Nut. The first Silom section ran from National Stadium to Saphan Taksin. Later work made both lines much longer. Their basic form, however, stayed the same. BTS is an elevated railway built along major urban roads.
BTS says its viaduct is usually about 12 metres above the road median. The Sukhumvit Line follows a long urban axis through the north, centre, and southeast of the metro area. The Silom Line links Thonburi with Sathorn, Silom, and Siam. It also crosses the Chao Phraya near Saphan Taksin. The tracks are so part of Bangkok's street view.
The core MRT name is รถไฟฟ้ามหานคร / Metropolitan Rapid Transit. MRTA develops the MRT project family. These lines do not all use the same type of railway.
The รถไฟฟ้ามหานคร สายเฉลิมรัชมงคล / M. R. T. Chaloem Ratchamongkhon Line is the Blue Line. Its first section opened in 2004. It was Thailand's first underground metro. The full line now includes both underground and elevated track.
In central Bangkok, the Blue Line runs below streets and dense districts. It passes Hua Lamphong, Charoen Krung, Wang Burapha, and Sanam Chai. It also goes under the Chao Phraya. Farther west and north, parts of the route are elevated. Blue is so not only a subway.
The รถไฟฟ้ามหานคร สายฉลองรัชธรรม / Chalong Ratchadham Line is the Purple Line. It is elevated heavy rail. The line links Nonthaburi with northern Bangkok. It follows Khlong Bang Phai, Rattanathibet, Nonthaburi Civic Center, Tiwanon, and Tao Poon. It crosses the Chao Phraya near Phra Nang Klao. The line opened in 2016.
The Nakkhara Phiphat / Yellow Line uses an elevated monorail. It follows Lat Phrao, Bang Kapi, Srinagarindra, Thepharak, and Samrong. The Wiwat Nakhon / Pink Line is also an elevated monorail. It crosses the northern metro area through Nonthaburi, Pak Kret, Chaeng Watthana, Government Complex, Ram Inthra, and Min Buri.