The calculated distance (air line) between Kampong Thom and Siem Reap is approximately 83 miles respectively 133 kilometers.
By car or train, the actual journey to Siem Reap is certainly longer, as only the direct route (as the crow flies) between Kampong Thom and Siem Reap has been calculated here.
Air line (approximately)
133 kilometers
72 nautical miles