The calculated distance (air line) between Cologne and Mechelen-aan-de-Maas is approximately 55 miles respectively 88 kilometers.
By car or train, the actual journey to Mechelen-aan-de-Maas is certainly longer, as only the direct route (as the crow flies) between Cologne and Mechelen-aan-de-Maas has been calculated here.
Air line (approximately)
88 kilometers
48 nautical miles