The calculated distance (air line) between Navan and Dún Laoghaire is approximately 33 miles respectively 54 kilometers.
By car or train, the actual journey to Dún Laoghaire is certainly longer, as only the direct route (as the crow flies) between Navan and Dún Laoghaire has been calculated here.
Air line (approximately)
54 kilometers
29 nautical miles