The calculated distance (air line) between Ouderkerk aan de Amstel and Amersfoort is approximately 23 miles respectively 36 kilometers.
By car or train, the actual journey to Amersfoort is certainly longer, as only the direct route (as the crow flies) between Ouderkerk aan de Amstel and Amersfoort has been calculated here.
Air line (approximately)
36 kilometers
20 nautical miles