's YouTube unit says it now reaches 1.5 billion viewers every month -- and its users watch more than an hour of mobile videos per day -- as it expands its video programming to sell more digital ads.

YouTube CEO Susan Wojcicki shared the news in a blog post the same day she gave a keynote address at VidCon, a conference for online video creators in Anaheim, California.

Google CEO Sundar Pichai tweeted about the milestone soon after Wojcicki's post: tweet

Wojcicki also wrote that YouTube Red, the company's foray into original videos, has launched 37 series that have generated "nearly a quarter billion views."

YouTube Red has 12 new projects in the works, she said.