If the Google+ invites keep flowing, the search giant's social-networking site could reach 10 million users by day's end and 20 million by the end of the weekend, according to Tuesday analysis.
In an attempt to get a rough estimate of Google+ users, Ancestry.com founder Paul Allen (not to be confused with the Microsoft co-founder) has been comparing US Census Data with last names of certain Google+ members. Early estimates released over the weekend put Google+ at about 4.5 million users, but that has since exploded, Allen said.
"My surname-based analysis shows that the number of Google+ users worldwide reached 7.3 million yesterday (July 10)—up from 1.7 million users on July 4th," Allen wrote in a Google+ post. "That is a 350% increase in six days. The userbase is growing so quickly that it is challenging for me to keep up, since the number of users of any given surname (even the rare ones I am tracking) seems to be climbing every day."
More impressive, he said, is that it appears approximately 2.2 million people have joined Google+ in the last 32 to 34 hours, for a total of about 9.5 million people on Monday, Allen speculated.
Check out our Google+ ReviewAs a result, he expects user numbers to grow to 10 million today and 20 million by the weekend, provided invites remain open. "As one G+ user put it, it is easy to underestimate the power of exponential growth," Allen wrote.
How exactly is Allen getting these numbers? He said he looked at US Census Bureau data about the popularly of last names in the U.S. and the compared it with the number of Google+ users who had the same last names.
"By using a sample of 100-200 surnames, I am able to accurately estimate the total percentage of the U.S. population that has signed up for Google+," he wrote. "Then I use that number and a calculated ratio of U.S. to non-U.S. users to generate my worldwide estimates."
Currently, his ratio is 1 U.S. user for every 2.12 non-U.S. Google+ user, a ratio that has not been updated since July 4. "That is definitely a weakness in my model that I hope to address soon. The ratio will likely change over time," Allen said.
He acknowledged that this is not a perfect method, but said it was sound. "If I had resources to include 500 or 1,000 surnames in my sample, then I believe my model would be more accurate. But my time and budget available for this project are small, so it is what it is," he wrote.
Google, meanwhile, is staying mum. "We don't have any comment on the number of people in the Google+ Field Trial," a Google spokeswoman said yesterday. When it re-opened Google+ invites recently, the company said it wanted to double the number of people in its "field trial," but declined to say exactly how many people that entailed.
Facebook, meanwhile, recently confirmed that it now has 750 million users, but CEO Mark Zuckerberg said the company didn't publicize the milestone because user numbers are not as important as they once were.
For more, see PCMag's full hands-on with Google+, the slideshow below, as well as 6 Things Google+ Can Do That Facebook Can't and Social Networking Showdown: 8 Facebook Features Google+ Doesn't Have (Yet). On privacy, see Google+ Privacy: Has Google Learned Its Lesson?