The calculated distance (air line) between Trá Mhór and Dún Laoghaire is approximately 89 miles respectively 143 kilometers.
By car or train, the actual journey to Dún Laoghaire is certainly longer, as only the direct route (as the crow flies) between Trá Mhór and Dún Laoghaire has been calculated here.
Air line (approximately)
143 kilometers
77 nautical miles