The calculated distance (air line) between Al Khafjī and As Saffānīyah is approximately 35 miles respectively 57 kilometers.
By car or train, the actual journey to As Saffānīyah is certainly longer, as only the direct route (as the crow flies) between Al Khafjī and As Saffānīyah has been calculated here.
Air line (approximately)
57 kilometers
31 nautical miles