The calculated distance (air line) between Sievierodonetsk and Kostiantynivka is approximately 46 miles respectively 74 kilometers.
By car or train, the actual journey to Kostiantynivka is certainly longer, as only the direct route (as the crow flies) between Sievierodonetsk and Kostiantynivka has been calculated here.
Air line (approximately)
74 kilometers
40 nautical miles