Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 15:00 and arrives at Koh Samui Samui International Airport at 16:30.
The flighttime is about 1h 30m. The distance travelled ("as the bird flies"): 113 Km. So the average speed is roughly 75 Km.
The best day to arrive at Bangkok is Wednesday and it would be best to avoid Friday, as prices are on average 67.66% higher than on Wednesday. (Average prices, based on 5445466 datapoints.)
We have a lot more statistics for flights PG 157 and between Bangkok and Koh Samui.
