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