The calculated distance (air line) between Sauðárkrókur and Mosfellsbær is approximately 125 miles respectively 201 kilometers.
By car or train, the actual journey to Mosfellsbær is certainly longer, as only the direct route (as the crow flies) between Sauðárkrókur and Mosfellsbær has been calculated here.
Air line (approximately)
201 kilometers
108 nautical miles