The calculated distance (air line) between Mattersburg and Klagenfurt am Wörthersee is approximately 125 miles respectively 201 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 Mattersburg and Klagenfurt am Wörthersee has been calculated here.
Air line (approximately)
201 kilometers
108 nautical miles