The cheapest way in. The Private transfer to Potsdam is 7 minutes quicker for €131 more, which is not worth it at this party size.
RB22 regional train
RB22 · DB Regio, on a VBB ticketPickup, hours & luggage
Boards at. Flughafen BER station, beneath Terminal 1
The same ABC single at EUR 5.00, and the same 4-Fahrten-Karte arithmetic as every other train here — Potsdam is zone C, same as the airport.
Luggage. A regional train, with space at the carriage ends.
Hours. Hourly, all day.