The calculated distance (air line) between Bourg-la-Reine and Boulogne-Billancourt is approximately 5 miles respectively 8 kilometers.
By car or train, the actual journey to Boulogne-Billancourt is certainly longer, as only the direct route (as the crow flies) between Bourg-la-Reine and Boulogne-Billancourt has been calculated here.
Air line (approximately)
8 kilometers
5 nautical miles