One hundred forty characters is about the length of a headline. To get a sense of what that feels like, type up a message in the "What are you doing?" box. As you type, the Twitter website counts down your remaining characters (look just above the box where you're typing). If you're on a phone, remember to use just 140 of the 160 characters in your outgoing texts.

As you can see here, 140 characters is approximately a sentence, maybe two. Bear in mind that your 140 characters includes spaces.

By the way, posts on Twitter are capped at 140 characters for a reason: text messages on your phone are limited to just 160 characters. Twitter takes that base and reserves 20 characters for usernames, leaving you with a tidy 140.