The study analysed 1.5 billion tweets sent by 70 million users in one month to work out where people were.
On average, it found, people who mentioned or retweeted each other's messages were 750 miles apart.
The study also revealed that people tweeting each other the most tended to be the furthest apart.
The study, by Kalev Leetaru and colleagues at the University of Illinois, did not look at the textual content of tweets but attempted to work out where 70 million users of the service were located last October and November when they sent them.
Then Mr Leetaru and his co-researchers plotted who was communicating with whom to get a sense of the geographic distances dividing people who regularly chat via the microblogging service.
The study, published in the online journal First Monday, found that, on a typical day, the average tweet is just nine words long and 85% of those messages originate with just 15% of users."