The calculated distance (air line) between Katwijk aan den Rijn and Haarlem is approximately 16 miles respectively 25 kilometers.
By car or train, the actual journey to Haarlem is certainly longer, as only the direct route (as the crow flies) between Katwijk aan den Rijn and Haarlem has been calculated here.
Air line (approximately)
25 kilometers
14 nautical miles