Booking your Rome airport transfers in advance for peace of mind especially if you have another plane to catch in the other Rome airport.
From my own experience, I had plenty of time to get from the Ciampino airport to the Fiumicino airport.
But… I hadn’t booked anything in advanced, made a mess of it all and to cut a long story short I missed my connecting flight to Sardegna.
You will of course find taxis services outside of each Rome airport as well as Buses for your transfer, but personally I believe it is always best to be on the safe side and book a transfer in advance.
You can book bus a transfer online with Terravision. The price of an all around trip would be 16 Euro’s per person.
Note that the bus transfer from each Rome airport will take you to the main bus station in Rome city centre where you will find the connection bus to forward your transfer.
Depending on how many of you are travelling , you may also want to check the hassle free transfer option of booking a taxi.
I found this website that is so simple to calculate and see just how much it will cost for an airport to airport transfer in Rome.
They also have minibuses if you are travelling with a large group.
I made a mess of my own Rome airport transfer so I haven’t got any personal positive advice apart from I wished I had booked my transfer in advance.
You may what to check the Rome Taxi Forum discussions in Tripadvisor for more suggestions from people that had hands on experience with Rome taxi companies.