The calculated distance (air line) between Phnom Penh and Kampong Speu is approximately 28 miles respectively 45 kilometers.
By car or train, the actual journey to Kampong Speu is certainly longer, as only the direct route (as the crow flies) between Phnom Penh and Kampong Speu has been calculated here.
Air line (approximately)
45 kilometers
24 nautical miles