The calculated distance (air line) between Néa Erythraía and Petroúpolis is approximately 8 miles respectively 13 kilometers.
By car or train, the actual journey to Petroúpolis is certainly longer, as only the direct route (as the crow flies) between Néa Erythraía and Petroúpolis has been calculated here.
Air line (approximately)
13 kilometers
7 nautical miles