The calculated distance (air line) between Mosfellsbær and Reykjanesbær is approximately 28 miles respectively 46 kilometers.
By car or train, the actual journey to Reykjanesbær is certainly longer, as only the direct route (as the crow flies) between Mosfellsbær and Reykjanesbær has been calculated here.
Air line (approximately)
46 kilometers
25 nautical miles