The calculated distance (air line) between Ouderkerk aan de Amstel and Alkmaar is approximately 24 miles respectively 39 kilometers.
By car or train, the actual journey to Alkmaar is certainly longer, as only the direct route (as the crow flies) between Ouderkerk aan de Amstel and Alkmaar has been calculated here.
Air line (approximately)
39 kilometers
21 nautical miles