The calculated distance (air line) between Sant Martí and Sants-Montjuïc is approximately 4 miles respectively 6 kilometers.
By car or train, the actual journey to Sants-Montjuïc is certainly longer, as only the direct route (as the crow flies) between Sant Martí and Sants-Montjuïc has been calculated here.
Air line (approximately)
6 kilometers
3 nautical miles