The calculated distance (air line) between Ar Rumaythīyah and Al Khafjī is approximately 65 miles respectively 105 kilometers.
By car or train, the actual journey to Al Khafjī is certainly longer, as only the direct route (as the crow flies) between Ar Rumaythīyah and Al Khafjī has been calculated here.
Air line (approximately)
105 kilometers
57 nautical miles