WP - Change excerpt length in Wordpress

There is more than one way to change the excerpt length in a Wordpress Post.
I collected all the working methods to change the default excerpt (55) to however you need.

Solution 1 - Excerpt length in “wp-includes”
PROS: Fast and easy.
CONS: This will be applied to every category and archive, incluiding the blog homepage.
Source: It’s Called Web Design
Go into “wp-includes/formatting.php”, line 1333 (line 853 for version prior to 2.7).
Change “55″ according to [...]