The calculated distance (air line) between Néa Kallikráteia and Níkaia is approximately 165 miles respectively 266 kilometers.
By car or train, the actual journey to Níkaia is certainly longer, as only the direct route (as the crow flies) between Néa Kallikráteia and Níkaia has been calculated here.
Air line (approximately)
266 kilometers
143 nautical miles