The calculated distance (air line) between Kostanjevica na Krki and Mengeš is approximately 46 miles respectively 75 kilometers.
By car or train, the actual journey to Mengeš is certainly longer, as only the direct route (as the crow flies) between Kostanjevica na Krki and Mengeš has been calculated here.
Air line (approximately)
75 kilometers
40 nautical miles