The calculated distance (air line) between Smach Mean Chey and Kampong Thom is approximately 149 miles respectively 239 kilometers.
By car or train, the actual journey to Kampong Thom is certainly longer, as only the direct route (as the crow flies) between Smach Mean Chey and Kampong Thom has been calculated here.
Air line (approximately)
239 kilometers
129 nautical miles