Measure Your Impact with Analytics.Twitter.com
Measure your tweet activity by using Twitter’s Analytical tool. The tool will measure your how successful your tweets are by measuring impressions and engagements. An Impression is the number of times a user saw your tweet and an engagement is how many times a user has interacted with your tweet.
The tool also shows demographics of your followers, their interests and locations. Free and easy to use just sign in at analytics.twitter.com.