"An estimated three billion people will watch the ceremony". This lazy assumption has peppered BBC output (and others worldwide) for the last three days.
Let's go back to the stats for the London Olympics, published by the Olympic movement itself with a view to keeping sponsors happy. That calculated that coverage of the games was available in 4.8 billion households, and then says that "A projected 3.6 billion viewers saw at least one minute of London 2012 coverage on television". The italics are mine; note again, this is one minute of the total coverage of the whole event, not just the opening, which added up to 99, 982 hours of broadcasting - stretched out that would last for eleven years.
The UN estimate of current total world population is 7.4 billion. Let's guess that one third might have been asleep at the time. To hit the BBC News estimate, 3 out of every 4 people awake would be required to watch some of the ceremony.