Anywhere from 10'-16'+. Depends on what AndrewH said in a previous thread, food intake, genetics, and other things.

And being in Chicago I know the law on large constrictors, somewhat. I am informing you about it now. You cannot keep a snake that is over 6' or 8', I keep forgetting which one. BUT, I have also heard that there is a by-law that is the snake is in a LOCKED cage, it is ok to keep. But once it is out, it is illegal.