Unless otherwise noted, movies are playing at most multiplex cinema chains. For showtimes, call the cinemas or check their websites.
Seat prices in Bangkok cinemas are usually around 140 baht and range from 80 baht to 1,000 baht (or more, for seats in luxury "Gold Class", "Blue Ribbon" or "First Class" cinemas). Major Cineplex and SF Cinema branches have special low prices on Wednesdays, but there are many restrictions.
The King’s Anthem is played before the main program. You must stand as a sign of respect.
Here are the contact details for Bangkok cinemas:
Apex Siam Square (Lido and Scala)
Rama 1 Road
Century – The Movie Plaza
BTS: Victory Monument
Embassy Diplomat Screens
6th floor, Central Embassy
3rd floor, RCA Plaza (above Tops Supermarket)
MRT: Phetchaburi, exit 1, then taxi to RCA
Krungsri IMAX, Paragon Cineplex (BTS: Siam)
IMAX Digital, Major Cineplex Ratchayothin
MRT: Phaholyothin, exit 3, then taxi
IMAX Digital, Major Cineplex Pinklao
554-544/1 Borom Rachachonnanee Road,
Bang Bamru, Bang Phlat Bangkok 10700
River Express to Phra Pin Klao Bridge and then taxi
Major Cineplex (includes EGV, Esplanade, IMAX, Mega, Paradise, Paragon)
Siam Paragon: +6621294635
SF Cinema City, SFX Cinema, SF World Cinema
There's also a list of Bangkok cinemas on Foursquare.