The calculated distance (air line) between Bochum-Hordel and Erftstadt is approximately 50 miles respectively 81 kilometers.
By car or train, the actual journey to Erftstadt is certainly longer, as only the direct route (as the crow flies) between Bochum-Hordel and Erftstadt has been calculated here.
Air line (approximately)
81 kilometers
44 nautical miles