The calculated distance (air line) between Nakhon Phanom and Nong Khai is approximately 138 miles respectively 222 kilometers.
By car or train, the actual journey to Nong Khai is certainly longer, as only the direct route (as the crow flies) between Nakhon Phanom and Nong Khai has been calculated here.
Air line (approximately)
222 kilometers
120 nautical miles