Google+’s “unofficial statistician” Paul Allen believes that Google+ now has over 43 million users. Allen, whose name you might know as being the founder of Ancestry.com has a method whereby he estimates the total number of users on Google+ based upon uncommon surnames.

In the past, Allen has been startlingly accurate:

  • July 4th – 1.7 million users
  • July 9th – 4.5 million users
  • July 12 – 10 million users
  • September 9th – 28.7 million users
  • September 22nd – 43.4 million users

Way to go Google!

In the past couple of days, since Google opened its doors to the general public over age 18, the growth rate has skyrocketed to rates we only saw during the first week of its “field test” — back when it had a small number of users to begin with, the growth rates were of course much higher.

But when I checked the data this morning, it is clear that Google+ is absolutely exploding — 30% growth in just 2 days and with a base of nearly 30 million members already.

Here are my latest estimates:

On September 9, our model showed 28.7 million users
This morning, our model shows 37.8 million users, with most of the growth coming in the last 2 days
By adding a fudge factor (see below) to account for private user profiles and for non-Roman surnames (both of which are totally overlooked by our surname counting model), my current estimate is 43.4 million users