I know you've either asked this question, or been asked this question: How do you measure your social media efforts? Some people just don't, or say that there is no way to measure social media. I agree that it is a challenge, but it's not impossible. And with websites like tweetreach.com popping up left and right, it's becoming easier and easier everyday.
Tweetreach.com allows you to search for a user name, a URL, a phrase, or a hashtag, and this website will analyze the tweets that match your search. Before you know it you have reach and exposure data for the tweet in question. It gives you the amount of impressions, and what type of tweet it was (@reply, retweet, or regular tweet), and provides you with pretty little pie charts (example below) to display the data.
So get your tweetreach on and find out how far your tweets have gone!