Hangouts are limited to 10 video conference participants, with no time limit. You can also use Hangouts On Air to broadcast a hangout to many more people, though there is still a limit of 10 active participants.

If you activate Google+ premium features, the limit increases to 15 participants for both Hangouts and Hangouts On Air. The limit remains at 10, however, for Hangouts created from the Google+ Events page.