A little over a week ago Facebook reached a major milestone: 300 million active users. The fastest-growth region continues to be Asia, but growth in other overseas regions such as the Americas and Africa have also been strong. Currently reaching only 1% of potential users in Asia and Africa, Facebook has barely scratched the surface in both regions:

Growth in the U.S. remains fastest among those age 45 and older, and the share of those users is higher in the U.S. than overseas. In other regions recent growth tended to be more evenly divided among age groups. One notable exception has been the teen group in Asia, which grew over 80% in the last 12 weeks.

Of the 300 million users, how many are actively using Facebook right now? (For the rest of this post active means not just logged in, but actually engaged.) By treating the previous question as a Fermi problem^†, I can probably derive a decent estimate. First, I assume that the average fraction of people actively using Facebook at any moment, equals the fraction of time an average Facebook user is active on the site^††. Without access to any usage stats, I'll throw out the following guesstimate: a typical Facebook user spends 4 hours per month (or 48 per year) actively using the site.

Depending on how accurate you want to be, there are 1.6 to 6 million people actively using Facebook right now. If the average Facebook user spends considerably more than 4 hours per month (actively) using the site, the estimate would be much higher than a 1.6 million. I do have an escape clause: in classic Fermi problems, being within a factor of 10 is considered acceptable.

(†) Increasingly popular in the business world, Fermi problems have long been staples in Physics (and Math) departments.
(††) In other words, if the average Facebook user spends 1% of her time actively using the site, on average 1% of all Facebook users are actively using the site at any given moment.

A little over a week ago Facebook reached a major milestone: 300 million active users. The fastest-growth region continues to be Asia, but growth in other overseas regions such as the Americas and Africa have also been strong. Currently reaching only 1% of potential users in Asia and Africa, Facebook has barely scratched the surface in both regions:

Growth in the U.S. remains fastest among those age 45 and older, and the share of those users is higher in the U.S. than overseas. In other regions recent growth tended to be more evenly divided among age groups. One notable exception has been the teen group in Asia, which grew over 80% in the last 12 weeks.

Of the 300 million users, how many are actively using Facebook right now? (For the rest of this post active means not just logged in, but actually engaged.) By treating the previous question as a Fermi problem^†, I can probably derive a decent estimate. First, I assume that the average fraction of people actively using Facebook at any moment, equals the fraction of time an average Facebook user is active on the site^††. Without access to any usage stats, I'll throw out the following guesstimate: a typical Facebook user spends 4 hours per month (or 48 per year) actively using the site.

Depending on how accurate you want to be, there are 1.6 to 6 million people actively using Facebook right now. If the average Facebook user spends considerably more than 4 hours per month (actively) using the site, the estimate would be much higher than a 1.6 million. I do have an escape clause: in classic Fermi problems, being within a factor of 10 is considered acceptable.

(†) Increasingly popular in the business world, Fermi problems have long been staples in Physics (and Math) departments.
(††) In other words, if the average Facebook user spends 1% of her time actively using the site, on average 1% of all Facebook users are actively using the site at any given moment.