The calculated distance (air line) between Galway and Dún Laoghaire is approximately 120 miles respectively 194 kilometers.
By car or train, the actual journey to Dún Laoghaire is certainly longer, as only the direct route (as the crow flies) between Galway and Dún Laoghaire has been calculated here.
Air line (approximately)
194 kilometers
105 nautical miles