The calculated distance (air line) between Tallaght and Dún Laoghaire is approximately 10 miles respectively 16 kilometers.
By car or train, the actual journey to Dún Laoghaire is certainly longer, as only the direct route (as the crow flies) between Tallaght and Dún Laoghaire has been calculated here.
Air line (approximately)
16 kilometers
9 nautical miles