The calculated distance (air line) between Sint-Pieters-Leeuw and Antwerpen is approximately 31 miles respectively 50 kilometers.
By car or train, the actual journey to Antwerpen is certainly longer, as only the direct route (as the crow flies) between Sint-Pieters-Leeuw and Antwerpen has been calculated here.
Air line (approximately)
50 kilometers
27 nautical miles