Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 08:10 and arrives at Koh Samui Samui International Airport at 09:20.
The flighttime is about 1h 10m. The distance travelled ("as the bird flies"): 113 Km. So the average speed is roughly 97 Km.
The best day to arrive at Bangkok is Wednesday and it would be best to avoid Friday, as prices are on average 42.6% higher than on Wednesday. (Average prices, based on 5450320 datapoints.)
We have a lot more statistics for flights PG 123 and between Bangkok and Koh Samui.
