The calculated distance (air line) between Zürich (Kreis 4) / Aussersihl and Luzern is approximately 25 miles respectively 40 kilometers.
By car or train, the actual journey to Luzern is certainly longer, as only the direct route (as the crow flies) between Zürich (Kreis 4) / Aussersihl and Luzern has been calculated here.
Air line (approximately)
40 kilometers
21 nautical miles