The calculated distance (air line) between Udon Thani and Phitsanulok is approximately 172 miles respectively 276 kilometers.
By car or train, the actual journey to Phitsanulok is certainly longer, as only the direct route (as the crow flies) between Udon Thani and Phitsanulok has been calculated here.
Air line (approximately)
276 kilometers
149 nautical miles