miles required to upgrade seats in Thai Airways

miles required to upgrade seats in Thai Airways depend on the flight distance and you tickets booking class

Thai Airways frequent flyer program Royal Orchid Plus gives you Awards both in the air and on the ground.
Air and Upgrade Awards with THAI and Star Alliance airlines, Hotel Awards, Excess Baggage Awards with THAI and a range of other redemption options with Promotional Awards.
Royal Orchid Plus Awards can be redeemed by members, and for any of their Award Nominees.
Each member’s personal Award Nominee List can contain up to five names, and additions or changes can be completed instantly online.

for Destinations from 8,001 - 12,500 miles:
such as flight from Bangkok to Los Angeles
you need 40000 to 50000 miles to upgrade from economy class to Royal Silk Class business class seats
you need 80000 miles to upgrade from deep discount economy class tickets to business class

Economy Class to Premium Economy Class require about 20000 to 30000 miles

Mileage Upgrades One way One sector
Economy Class
(G, V, W Y, B, M H, Q, S, T, K) to Premium Economy Class (G, V, W)
Premium Economy Class (U)to Royal Silk Class seats
business class to Royal First Class
(C, D, J)
Destinations from 3,601 - 4,800 miles:
Between Bangkok and Brisbane, Melbourne, Moscow, Sydney

Destinations from 4,801 - 8,000 miles:
Between Bangkok and europe: Athens, Auckland, Copenhagen, Frankfurt, London, Madrid, Milan, Munich, Oslo, Paris, Rome, Stockholm, Zurich

38,000 to 50,000 miles
Mileage Upgrade Awards charts

http://www.thaiair.com/frequent-flyer/en/mileage-upgrade-awards-on-thai.htm