Nielsen, the ratings service, announced Tuesday that it will begin to tabulate how many people get their live TV from Hulu and YouTube, an effort to provide a more accurate picture of how many people now watch broadcast networks by streaming them, rather than watching them on traditional TV.

Hulu and YouTube have not revealed how many people have subscribed for the live TV services that they launched in the spring as a counter to cable TV.

Subscribers can stream channels live on laptops, smartphones and elsewhere. They can also record shows digitally or watch them on demand. Both services cost nearly $40 a month.

Media companies base the amount they charge advertisers on the number of people who are watching at a particular time, and want to insure that online viewers are also counted as more people shift to using online streaming services.