First of all; Bangkok has 2 different airports. Suvarnabhumi, the new modern airport for mainly intercontinental flights and Don Muang, the old airport mainly for domestic budget flights. A common mistake by travellers is to order a taxi and just say “airport”. The result is that many people end up on the wrong airport. Same counts for bus station. Bangkok doesn’t have a main bus station but around 4 different major bus stations.
Suvarnabhumi airport – Don Muang airport
If you end up on the wrong airport or you need a connecting flight from another airport there is a free of charge shuttle-bus between Suvarnabhumi and Don Muang. The shuttle bus journey time – dependent on Bangkok’s frequent traffic jams – is about one hour. The distance by road is around 45km.