The calculated distance (air line) between Jablonec nad Nisou and Třinec is approximately 171 miles respectively 275 kilometers.
By car or train, the actual journey to Třinec is certainly longer, as only the direct route (as the crow flies) between Jablonec nad Nisou and Třinec has been calculated here.
Air line (approximately)
275 kilometers
148 nautical miles