The calculated distance (air line) between Dortmund and Knokke-Heist is approximately 181 miles respectively 292 kilometers.
By car or train, the actual journey to Knokke-Heist is certainly longer, as only the direct route (as the crow flies) between Dortmund and Knokke-Heist has been calculated here.
Air line (approximately)
292 kilometers
157 nautical miles