There are
2,635 mi
from Gaithersburg, MD to Simi Valley, CA
That's the driving distance. It would take 1 day 23 hours to go from Gaithersburg, Maryland to Simi Valley, California.
The flight distance (direct flight from Gaithersburg, MD to Simi Valley, CA) is 2,307.40 mi.
2,635 mi = 4,240.69 kms