Ashkar

Adds an Excerpt Length field setting to the Reading Settings section of your WordPress dashboard. This setting allows you to specify the number of words that you want to display in the <code><a href="https://codex.wordpress.org/Template_Tags/the_excerpt" rel="external">the_excerpt()</a></code> function.

Change Excerpt Length

Allows users to change the excerpt length from the WordPress Reading Settings page.

The Krotek

Adds Excerpt Length option on Reading page, which can be used to set the number of words in post excerpt.
FEATURES
<ul>
<li>Allows you to set custom excerpt length.</li>
<li>Will override the same filter in templates or other plugins (always works).</li>
</ul>
More information can be found on <a href="https://thekrotek.com/wordpress-extensions/miscellaneous" rel="nofollow ugc">extension’s page</a>.

Custom Excerpt Length

Adds Excerpt Length option on Reading page, which can be used to set the number of words in post excerpt.

Change Excerpt Length vs Custom Excerpt Length