The calculated distance (air line) between Kampong Thom and Sihanoukville is approximately 172 miles respectively 277 kilometers.
By car or train, the actual journey to Sihanoukville is certainly longer, as only the direct route (as the crow flies) between Kampong Thom and Sihanoukville has been calculated here.
Air line (approximately)
277 kilometers
149 nautical miles