The new limit will not apply to tweets written in Japanese, Chinese and Korean which can convey more information in a single character.
The move follows a trial among a small group of users which started in September in response to criticism that it was not easy enough to tweet.
The change is part of Twitter's plan to attract new users and increase growth.
Twitter brevity
During the test, only 5% of tweets sent were longer than 140 characters and only 2% more than 190, the social media site said in a blog post.
