The calculated distance (air line) between San Diego de la Unión and San Luis Potosí is approximately 48 miles respectively 77 kilometers.
By car or train, the actual journey to San Luis Potosí is certainly longer, as only the direct route (as the crow flies) between San Diego de la Unión and San Luis Potosí has been calculated here.
Air line (approximately)
77 kilometers
41 nautical miles