The calculated distance (air line) between Leoben and Klagenfurt am Wörthersee is approximately 64 miles respectively 103 kilometers.
By car or train, the actual journey to Klagenfurt am Wörthersee is certainly longer, as only the direct route (as the crow flies) between Leoben and Klagenfurt am Wörthersee has been calculated here.
Air line (approximately)
103 kilometers
55 nautical miles