The calculated distance (air line) between San Luis Potosí and San Miguel de Allende is approximately 87 miles respectively 139 kilometers.
By car or train, the actual journey to San Miguel de Allende is certainly longer, as only the direct route (as the crow flies) between San Luis Potosí and San Miguel de Allende has been calculated here.
Air line (approximately)
139 kilometers
75 nautical miles