The calculated distance (air line) between Agios Ioannis Rentis and Chalkída is approximately 35 miles respectively 56 kilometers.
By car or train, the actual journey to Chalkída is certainly longer, as only the direct route (as the crow flies) between Agios Ioannis Rentis and Chalkída has been calculated here.
Air line (approximately)
56 kilometers
30 nautical miles