The International Olympic Committee estimates that almost 900 million people watched at least part of the London Games opening ceremony on television.
The IOC's television and marketing director Timo Lumme says it is the target figure for "global viewership ... that's all eyeballs across the world."
The final, official rating will be lower than 900 million. It counts viewers at home who watched for longer periods, and will be announced within months.
Lumme says around 80 of 200 national television markets have audited figures. Others are estimated.
Lumme says Usain Bolt's win in the 100-meter final on Sunday could reach an official rating of 200 million. It will likely be the sports event with the highest TV viewership at the London Games.