How Big Is Twitter Really?

It’s always been difficult to get a handle on the size of Twitter because as we learned earlier this week, 75 percent of its activity occurs outside via third-party desktop and mobile clients. But at least we could look at traffic as a proxy for the overall ecosystem and get a sense of growth trend by looking at data from outside traffic measurement services.

According to the latest numbers from comScore, for instance, attracted 79.4 million unique visitors worldwide in March, 2010, a 316 percent increase from a year ago. ComScore lists Twitter as the 30th largest site in the world now, bigger than Craigslist, Sony Online, and Expedia.

But wait a second. Twitter also disclosed for the first time earlier this week that it currently has 105 million registered users and 180 million unique visitors to I double-checked with Twitter, and a spokesperson confirmed the numbers are just for from Google Analytics. So that means comScore’s estimate is a little more than half what it should be. Talk about being way off.

At 180 million unique visitors per month, Twitter would rank No. 11 in comscore’s list of largest sites, right in between Tencent (172.8 million) and CBS Interactive (190.5 million). That is assuming, of course, that comScore’s estimates for everyone else is also correct. To be fair, no other measurement service got close to the 180 million either. And 75 percent of those users came from other clients, which makes it difficult to measure because they are clicking on links in desktop and mobile clients which then open up Web pages.

No matter how you slice it, Twitter is even bigger than anyone previously thought.