The calculated distance (air line) between Watermael-Boitsfort and Sint-Niklaas is approximately 28 miles respectively 45 kilometers.
By car or train, the actual journey to Sint-Niklaas is certainly longer, as only the direct route (as the crow flies) between Watermael-Boitsfort and Sint-Niklaas has been calculated here.
Air line (approximately)
45 kilometers
24 nautical miles