The calculated distance (air line) between Duisburg and Watermael-Boitsfort is approximately 111 miles respectively 178 kilometers.
By car or train, the actual journey to Watermael-Boitsfort is certainly longer, as only the direct route (as the crow flies) between Duisburg and Watermael-Boitsfort has been calculated here.
Air line (approximately)
178 kilometers
96 nautical miles