The calculated distance (air line) between San Sebastián de los Reyes and Tres Cantos is approximately 5 miles respectively 8 kilometers.
By car or train, the actual journey to Tres Cantos is certainly longer, as only the direct route (as the crow flies) between San Sebastián de los Reyes and Tres Cantos has been calculated here.
Air line (approximately)
8 kilometers
5 nautical miles