The calculated distance (air line) between Kostanjevica na Krki and Slovenj Gradec is approximately 49 miles respectively 78 kilometers.
By car or train, the actual journey to Slovenj Gradec is certainly longer, as only the direct route (as the crow flies) between Kostanjevica na Krki and Slovenj Gradec has been calculated here.
Air line (approximately)
78 kilometers
42 nautical miles