The calculated distance (air line) between Carrickmacross and Dún Laoghaire is approximately 53 miles respectively 85 kilometers.
By car or train, the actual journey to Dún Laoghaire is certainly longer, as only the direct route (as the crow flies) between Carrickmacross and Dún Laoghaire has been calculated here.
Air line (approximately)
85 kilometers
46 nautical miles