The calculated distance (air line) between That Phanom and Ubon Ratchathani is approximately 118 miles respectively 189 kilometers.
By car or train, the actual journey to Ubon Ratchathani is certainly longer, as only the direct route (as the crow flies) between That Phanom and Ubon Ratchathani has been calculated here.
Air line (approximately)
189 kilometers
102 nautical miles