The estimated audience from August 8-17 surpassed the 3.9bn viewers for the entire period of the Athens games in 2004 and the 3.6bn who watched the 2000 event in Sydney, said the company.
In an earlier report, Nielsen estimated that almost a third of the world's population - a little over 2bn - watched the opening ceremony of the Beijing Olympics.
It said the highest audience reach for the opening ceremony was in the Asia-Pacific, where more than five in 10 people tuned in, followed by Europe, where 30% of the population watched and North America at 24%. - Sapa-dpa