The calculated distance (air line) between Deir ez-Zor and Al Mayādīn is approximately 28 miles respectively 45 kilometers.
By car or train, the actual journey to Al Mayādīn is certainly longer, as only the direct route (as the crow flies) between Deir ez-Zor and Al Mayādīn has been calculated here.
Air line (approximately)
45 kilometers
24 nautical miles