The initial size is set to 8MB. I would never create TempDB data files with a size of 8 MB which in my opinion is really small for a data file even for small systems.
In most cases I would look at the size of the TempDB disk (because you create a desperate disk for TempDB right…) and fill up the entire disk with data files. In this case I would create 4 x 5 GB files to leave some space for the log file.
To properly set the initial size of the TempDB you still need to go through some checks how much your system might need.
Read the whole thing.