The calculated distance (air line) between Sezimovo Ústí and Třinec is approximately 180 miles respectively 289 kilometers.
By car or train, the actual journey to Třinec is certainly longer, as only the direct route (as the crow flies) between Sezimovo Ústí and Třinec has been calculated here.
Air line (approximately)
289 kilometers
156 nautical miles