Facebook has over a billion daily active users, so 100 million hours divided over 1 billion users is 0.1 hours/user which is 6 minutes per user. Seems reasonable. Of course, there are lots of people who don't watch any videos and on the flip side there are a lot of people who watch a lot of videos on facebook. Edit : as pointed out below, the autoplaying videos might skew the numbers quite a bit.