The calculated distance (air line) between Mosfellsbær and Kópavogur is approximately 7 miles respectively 12 kilometers.
By car or train, the actual journey to Kópavogur is certainly longer, as only the direct route (as the crow flies) between Mosfellsbær and Kópavogur has been calculated here.
Air line (approximately)
12 kilometers
6 nautical miles