Flight Leonardo da Vinci–Fiumicino Airport departs from Rome Leonardo da Vinci–Fiumicino Airport at 15:20 and arrives at San Francisco International Airport at 18:55.
The flighttime is about 12h 35m. The distance travelled ("as the bird flies"): 14957 Km. So the average speed is roughly 1189 Km.
There is an 9 hour time difference between Rome and San Francisco