The calculated distance (air line) between Watermael-Boitsfort and Berchem is approximately 27 miles respectively 43 kilometers.
By car or train, the actual journey to Berchem is certainly longer, as only the direct route (as the crow flies) between Watermael-Boitsfort and Berchem has been calculated here.
Air line (approximately)
43 kilometers
23 nautical miles