The calculated distance (air line) between Uccle and Heist-op-den-Berg is approximately 25 miles respectively 41 kilometers.
By car or train, the actual journey to Heist-op-den-Berg is certainly longer, as only the direct route (as the crow flies) between Uccle and Heist-op-den-Berg has been calculated here.
Air line (approximately)
41 kilometers
22 nautical miles