Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 19:25 and arrives at Koh Samui Samui International Airport at 20:30.
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 Sunday and it would be best to avoid Saturday, as prices are on average 42.25% higher than on Sunday. (Average prices, based on 5448595 datapoints.)
We have a lot more statistics for flights PG 183 and between Bangkok and Koh Samui.
