The calculated distance (air line) between Kostanjevica na Krki and Brežice is approximately 9 miles respectively 15 kilometers.
By car or train, the actual journey to Brežice is certainly longer, as only the direct route (as the crow flies) between Kostanjevica na Krki and Brežice has been calculated here.
Air line (approximately)
15 kilometers
8 nautical miles