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