The calculated distance (air line) between Néa Kallikráteia and Petroúpolis is approximately 160 miles respectively 258 kilometers.
By car or train, the actual journey to Petroúpolis is certainly longer, as only the direct route (as the crow flies) between Néa Kallikráteia and Petroúpolis has been calculated here.
Air line (approximately)
258 kilometers
139 nautical miles