The company that measures television viewership will soon begin counting people who watch programming through broadband in addition to the traditional broadcast or cable hook-up.

Nielsen's move is a significant step toward recognizing a world where the definition of TV viewing is swiftly changing and toward satisfying clients concerned that the company isn't keeping up with those changes. Separately, Nielsen is developing ways to track content on tablets and mobile phones.

For many years, roughly 99 percent of homes in the U.S. had televisions that received service through broadcast, cable or satellite signals.

Now the number of homes without such service is 4.2 percent - and growing each year. An estimated three-quarters of those homes still have TVs, however, and their owners watch programming through game consoles or services like Netflix and Amazon. Starting September, Nielsen will have meters that can monitor viewership in those homes, said Brian Fuhrer, a senior vice president at Nielsen.

This will add roughly 160 homes to Nielsen's current sample of 23,000 houses nationwide with meters monitoring viewing habits.

More significantly, Nielsen will return to its sample to find homes that have cable or broadcast, but also separate TV sets hooked up through broadband. This will add an estimated 2,000 more broadband sets, significantly increasing the sample size, Fuhrer said.

"Consumers are accessing content in new ways that fall outside of our traditional definitions and if we don't expand ... we could be missing an emerging trend," he said.