Originally Posted by Trajan
according to TG website ,"For THAI flights less than 500 miles in distance, you earn a minimum of 500 miles."
Thai website
Having done lots of Thai domestic flying I can confirm that you always get 500 miles minimum, with any destinations over 500 miles accruing additional actual mileage (e.g. BKK>HDY). Do remember though that you get NO bonus mileage for flying C-Class on domestic routes.