The calculated distance (air line) between Nieuwkerken-Waas and Leuven is approximately 31 miles respectively 51 kilometers.
By car or train, the actual journey to Leuven is certainly longer, as only the direct route (as the crow flies) between Nieuwkerken-Waas and Leuven has been calculated here.
Air line (approximately)
51 kilometers
27 nautical miles