The distance from Suvarnabhumi Airport to Khao San road in Bangkok is about 32 km, pure travel time is about 33 min. Not too far but it depends on the transport that you choose, your hotel location (the best hotels are here) and the current traffic in Bangkok.
SUVARNABHUMI AIRPORT LOCATION
Suvarnabhumi Airport Rail Link (ARL) is the cheapest way but you will have to take a connecting train to get to the city center of Bangkok. You can get off at Makkasan station (ticket 35 baht) and transfer to the MRT subway or you can get off at Phayathai station (ticket 45 baht) and transfer to the BTS Skytrain, both routes will take appx. 30 min. The train station is located in the terminal building, Level Basement B, tickets can be bought there. The Airport Rail Link Train works from 6 am to midnight.
The city bus is much cheaper than a taxi, but at the same time less convenient. The bus stops many times along the way and the trip can take up to 1 hr. The bus station is located in the terminal building, Level 1, outside the 7th Gate. Bus drivers sell tickets directly. The price is 60 baht.
The taxi counter is located on the Ground Floor (Level 1) of Suvarnabhumi airport next to entrances 3, 4, 7, 8. Taxi fares are metered. The extra charges are airport supercharge 50 baht and ExpressWay fare.
Make sure that the driver agrees to carry you according to the taximeter to avoid disputes later on. Some drivers try to set their own price on the grounds that the taximeter is broken.
PRIVATE TRANSFER FROM SUVARNABHUMI AIRPORT TO BANGKOK
The most convenient and fastest way to get to Bangkok is a private transfer. The driver will meet you at the arrival hall with a board with your name on it, take care of the luggage, and bring you right to your accommodation within appx. 30 min. No need to worry about the early or late flight arrival, the driver will monitor the actual arrival time if you choose the Meet & Greet option when booking a taxi.
The private transfer to Bangkok of 3 people and luggage starts from 654 baht for Toyota Corolla car class to 1017 baht for Toyota Camry or similar, a van will cost slightly more.
Should you arrive at Don Mueang Airport, please read this article about the transfer options. If you need to go from Suvarnabhumi airport to Don Mueang airport, read this guide first. The official Suvarnabhumi airport website is here.