We all know YouTube is the biggest video sharing site around, but how big is it, exactly, when compared to sites such as Facebook or Twitter? Here's a hint: YouTube has just hit one billion monthly unique users.

For comparison, Facebook hit that milestone in October 2012. It took the social network eight years to reach one billion active users — almost the exact amount of time as YouTube, which was founded in February 2005. Twitter, which has been around since March 2006, has more than 200 million monthly active users.

The YouTube team gives us a few more comparisons for good measure: "Nearly one out of every two people on the Internet visits YouTube. Our monthly viewership is the equivalent of roughly ten Super Bowl audiences. If YouTube were a country, we’d be the third largest in the world after China and India," says YouTube on its official blog.

YouTube also gives a more detailed insight on what's powering this growth in another blog post about Generation C and mobile devices. According to YouTube, Generation C (or Gen C) is a generation that has grown up consuming content "where and when they want". They watch YouTube on all screens; they constantly switch between devices, they're deeply engaged with online video and they thrive on community. Finally, they're curators — they care about finding content that's important to them.

Gen C, which YouTube considers to be its core audience, now watch just as much YouTube content on smartphones as they do on PCs, and 67% of Gen C watch YouTube on two devices or more, compared to 53% of the general population.

With the rise of smartphones, which have become the dominant force in the mobile phone industry in the last couple of years and show no signs of slowing down, YouTube needn't worry about maintaining this growth for at least another couple of years.

Image credit: YouTube