Managing Article Length in Drupal
If you create a particularly long article, Drupal manages the length by automatically shortening it for you and providing a Read More link if users want to read the entire article. Instead of showing a long post that takes up the entire screen, and making users scroll down to see any other content on the page, Drupal displays the first few sentences of the post.
When your post is really long, it can use up all of your screen real estate. The first post on the home page is fairly long, but it doesn't bump down the other posts on the page. The following illustration shows what this page would look like with the first post left untruncated.
There's nothing inherently wrong with having a long post, except it forces the visitors to your site to scroll down the page if they want to see additional content — and they might not bother. Therefore, it may be better to truncate the visible part of your post.
You can control how many characters Drupal displays when it truncates your articles. Follow these steps:
Log in to the site as the administrator.
Choose Structure→Content Types.
Click the Manage Display link to the right of Article and click the Teaser tab on the upper right.
The Article Manage Display settings form appears.
To change how many characters are displayed, click the Settings button to the right of Trim Length.
Change the value from the default 600 characters to whatever you choose.
To force Drupal to display entire articles rather than truncate them, choose Default from the Format drop-down list.
Click Update and then the Save button on the bottom left.
When you change the Trim Length of trimmed posts setting, it will also have an effect on articles that you have already published. Old articles will automatically be shortened to the new setting.