Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 07:30 and arrives at Koh Samui Samui International Airport at 08:35.
The flighttime is about 1h 05m. The distance travelled ("as the bird flies"): 113 Km. So the average speed is roughly 104 Km.
The best day to arrive at Bangkok is Tuesday and it would be best to avoid Sunday, as prices are on average 40.08% higher than on Tuesday. (Average prices, based on 5547009 datapoints.)
We have a lot more statistics for flights PG 121 and between Bangkok and Koh Samui.
