The calculated distance (air line) between Hafnarfjörður and Reykjanesbær is approximately 19 miles respectively 31 kilometers.
By car or train, the actual journey to Reykjanesbær is certainly longer, as only the direct route (as the crow flies) between Hafnarfjörður and Reykjanesbær has been calculated here.
Air line (approximately)
31 kilometers
17 nautical miles