Monday, July 25, 2011 at 9:03 am.

Facebook for iPhone now has 85 million active users, up 50% in 7 months

Facebook’s iPhone app just passed 85 million monthly active users, according to the Facebook for iPhone page. That’s up 50% from 7 months ago, around Christmas, when it had 57 million active users.

How about Facebook’s penetration among iOS devices? That is important, after all, as Facebook reportedly readies its own mobile app platform based around HTML5.

Apple recently announced that it has shipped 222 million iOS devices all-time. Even assuming that each iOS device shipped were still active, and belonged to a different Facebook user, Facebook for iPhone would be active on almost 40% of all the iOS devices. In reality, it’s probably a much higher penetration, given that many iOS devices have been retired, Facebook for iPad isn’t out yet, etc.

Facebook for Android, meanwhile, has almost 53 million monthly active users, according to AllFacebook’s stats. That’s up 150% from about 21 million around Christmas. It’s clearly growing much faster than Facebook for iPhone: 1.8 million new users per week versus 1.1 million, according to AllFacebook. And given Android’s recent milestone of 130 million devices, that suggests roughly 40% penetration, too.