Twitter marked the five-year anniversary of its first Tweet, sent by co-founder Jack Dorsey March 21, 2006, with a blog post by Carolyn Penner highlighting important Twitter numbers besides 140:

Five years ago this week, a small team of people started working on a prototype of the service that we now know as Twitter. On March 21, 2006, Jack Dorsey (@jack) sent the first Tweet.

Today, on every measure of growth and engagement, Twitter is growing at a record pace. Here are some numbers:

#tweets

3 years, 2 months and 1 day: The time it took from the first Tweet to the billionth Tweet.

1 week: The time it now takes for users to send 1 billion Tweets.

50 million: The average number of Tweets people sent per day, one year ago.

140 million: The average number of Tweets people sent per day, in the past month.

177 million: Tweets sent March 11, 2011.

456: Tweets per second (TPS) when Michael Jackson died June 25, 2009 (a record at that time).

6,939: Current TPS record, set four seconds after midnight in Japan on New Year’s Day.

#accounts

572,000: Number of new accounts created March 12, 2011.

460,000: Average number of new accounts per day over the past month.

182 percent: Increase in number of mobile users over the past year.

#employees

8, 29, 130, 350, 400: Number of Twitter employees in January 2008, January 2009, January 2010, January 2011, and today.