There are 150,000 taxis in Bangkok. All taxis are metered with the starting fee of 35 Baht for the first 3 kilometers and then 5 Baht per Kilometer. There are many taxi companies and various coloured taxis but costs and fares are the same.
Tipping the taxi driver when you finish your trip isn't necessary although rounding up the figure on the meter makes things easy for the driver to pay you quickly.
Let's say the meter comes to 90 Baht. In this instance, we'd probably just hand over a 100 Baht note and get out rather than rummaging around for the correct amount.
If the meter was 35 Baht, we'd hand over 40 Baht, but if the meter was 40 Baht, we'd just hand over 40 Baht.
We round up if we don't have the correct amount but even if we do, we still round up from say 37 to 40 or 42 to 45.
The different colours of Bangkok taxis represents the company rather than cost. All metered taxis must charge the same rate for distance traveled and / or time spent sitting in the taxi. A tariff chart usually hangs from the back of the driver's or passenger's seat so you can see the amount you can expect to pay. Presently, taxis do not give out any receipts but this will soon be introduced so you will be able to get a mini slip for the amount you have been charged. We've had one taxi provide us with one but it must have been a test taxi because we've not had one since.
Some of the colours are: Yellow and Green, Blue and Red, White and Red, Blue, Red, Pink as well as Orange.
Yellow and Green taxis used to be newer, but many have aged. The drivers own their vehicles and, if new, take care of their property.
Blue and Red taxis in Bangkok are rented from a taxi firm. Drivers rent the taxis for the day and because the drivers don't own them, they are less careful and you generally find that these drivers have less patience and in their driving. However, as a rule of thumb, the older the taxi, the patient the driver. Either that or the driver is really old and you take twice as long to get anywhere.
The other colours, or the single coloured Bangkok taxis, are all fairly new and you'll get a smoother ride.
Inside the taxi, on the door, is the taxi's number. This must be on display.
Taxis are available from departures and arrivals. At arrivals, there is a taxi stand immediately outside the airport, just walk up to the taxi meter counter, tell them your destination and they will present you with a yellow slip of paper which you then give to the driver standing in the queue to the right of the counter.
There is a 50 Baht surcharge for this service and does not cover toll fees if going by expressway. You will therefore pay the meter fee + 50 Baht + any tolls.
The only "problem" with taking one of those taxis is that it's very difficult to refuse a taxi that looks old. Once you have your ticket for your taxi, you take what you are given; old or new. It's a small issue for short journeys, but for long journeys, when it hot and the air-conditioning is not working and the car fumes are seeping into the cabin, it can make for a very long journey.
Alternatively, you can go to the arrivals section and try to get one of the taxis that has just dropped someone off. This will save you the 50 Baht surcharge.
Taxis queue up outside department stores
Various colours but same costs
Wait for the nicer looking taxis. If you don't like the look of the taxi that is stopping for you, wave it on and get a newer one. The ride will be more comfortable and the air conditioning will work better.
If grabbing a taxi late at night from a friend's place, get your friend to go to the taxi with you and go through the motions of taking a note of the taxi number. The number is not the license plate, but the number on the door outside the taxi, AND on a label attached to each door inside the taxi.
If traveling in a taxi alone, you might want to call a friend and tell them the taxi number. Drivers will pick up on the numbers you mention, even if you speak English, and you'll be less likely to be robbed but this is a fairly rare occurrence anyway.
Most taxis will have a photo of the driver, along with their license, placed on the dash-board of the taxi they are driving. If there is one, it's a good sign. If there isn't one, or the photo doesn't match the driver, then you might want to wait for a different taxi.