As part of Google’s announcement to acquire Snapseed’s creator Nik software, Vic Gundotra, the Senior Vice President of Engineering for Google, just announced a new milestone for Google+: 400 million registered users and 100 million monthly active users. He of course revealed the new statistic on Google+:

This week we also hit an important milestone–over 400,000,000 people have upgraded to Google+. It was only a year ago that we opened public sign-up, and we couldn’t have imagined that so many people would join in just 12 months. While Google+ is all about creating a better experience across Google, it’s also a destination. And here too, I’m happy to report that we have just crossed 100,000,000 monthly active users on Google+ (plus.google.com and mobile app).

It’s worth noting that Google+’s “unofficial statistician” Paul Allen predicted this milestone in January. In a posting titled “How Google+ Will Reach 400 Million Users In 2012″ on Google+, of course, he explained how Android, Chrome, YouTube, as well as Google+ APIs and developers will help push the social network to the milestone before the end of the year.

Yet the real story here isn’t the 400 million number, but the 100 million one. Google+’s main competitor Facebook doesn’t even bother talking about registered users because it knows the number is meaningless. The social networking giant only talks about monthly active users, of which it has 955 million as of June 30. Both Facebook and Google are talking about combined desktop and mobile users.

In fact, I’ve openly criticized Google for previously only sharing figures regarding registered users. The PR move resulted in many skewed comparisons between the two social networks. Now that we have comparable numbers though (assuming Google and Facebook have similar ways of describing a monthly active user), it’s now safe to say that Google+ is about one tenth the size of Facebook.

Image credit: stock.xchng