The calculated distance (air line) between Bochum-Hordel and Darmstadt is approximately 130 miles respectively 209 kilometers.
By car or train, the actual journey to Darmstadt is certainly longer, as only the direct route (as the crow flies) between Bochum-Hordel and Darmstadt has been calculated here.
Air line (approximately)
209 kilometers
113 nautical miles