Taxis in Bangkok are all metered. If asked to pay a fixed price decline and wait for the next (which won’t be far behind). Bangkok’s streets are swarming with taxis and it is unlikely you will wait long for a lift. The only exception to this is leaving the airport where a 50 baht surcharge is added. If using toll roads you will also need to pay the fee at the booth.
The bottom right corner of the taxi’s windscreen has a square red light. Light on means available. Light off means taken. Red light on with people inside means scammed. Try not to be one of these. If the taxi takes off without starting the meter let him know. If a taxi tries to scam you feel free to report them as here.
Taxi Fares: Taxis in Bangkok start with a fixed meter price of 35 baht and increments by 2 baht from there. Using taxis in Bangkok centre rarely you will rarely exceed 150 baht or 200 baht for the nearer outskirts. Peak time traffic can double these figures. At peak times it is best to avoid taxis where possible. This is when Bangkok’s quick and convenient Skytrain (BTS) and Underground (MRT) lines come in handy.
Suvarnabumi Airport: It is roughly 200baht up (plus 40 baht tollway charges) for taxis from central areas to Suvarnabumi Airport. For taxis leaving the airport there is an added 50 baht surcharge. Give yourself 1 hour travel time each way.