The calculated distance (air line) between Mechelen-aan-de-Maas and Leuven is approximately 44 miles respectively 70 kilometers.
By car or train, the actual journey to Leuven is certainly longer, as only the direct route (as the crow flies) between Mechelen-aan-de-Maas and Leuven has been calculated here.
Air line (approximately)
70 kilometers
38 nautical miles