The calculated distance (air line) between Zaanstad and Alphen aan den Rijn is approximately 23 miles respectively 38 kilometers.
By car or train, the actual journey to Alphen aan den Rijn is certainly longer, as only the direct route (as the crow flies) between Zaanstad and Alphen aan den Rijn has been calculated here.
Air line (approximately)
38 kilometers
20 nautical miles