The calculated distance (air line) between Néa Smýrni and Petroúpolis is approximately 7 miles respectively 11 kilometers.
By car or train, the actual journey to Petroúpolis is certainly longer, as only the direct route (as the crow flies) between Néa Smýrni and Petroúpolis has been calculated here.
Air line (approximately)
11 kilometers
6 nautical miles