The calculated distance (air line) between Rishon LeTsiyyon and Ashdod is approximately 15 miles respectively 24 kilometers.
By car or train, the actual journey to Ashdod is certainly longer, as only the direct route (as the crow flies) between Rishon LeTsiyyon and Ashdod has been calculated here.
Air line (approximately)
24 kilometers
13 nautical miles