There are
2,639 mi
from Simi Valley, CA to Gaithersburg, MD
That's the driving distance. It would take 1 day 23 hours to go from Simi Valley, California to Gaithersburg, Maryland.
The flight distance (direct flight from Simi Valley, CA to Gaithersburg, MD) is 2,307.40 mi.
2,639 mi = 3.22 kms