matteotrap

WordPress Excerpts should be short, you know.
But when a user writes a lot, you might want to limit the number of characters for the excerpt panel: that’s where the Excerpt Character Limiter plugin comes handy!
It will basically add a character countdown to the panel titlebar, and it will truncate the text when available characters drop to zero. 
Simple but effective!

Excerpt character limiter

It will basically add a character countdown to the panel titlebar, and it will truncate the text when available characters drop to zero.

Marcus Downing

Zaybiz

A simple plugin to enhance your use of the_excerpt() function. Allows you to change the default title and description of the excerpt box, add an excerpt box to pages and show a customizable jQuery character counter with the ability to limit the amount of characters.
The jQuery character counter from <a href="http://tomdeater.com/" rel="nofollow ugc">Tom Deater</a> provides a user friendly way to limit the amount of characters while writing.

Excerpt Tools

Change the default text and description of the excerpt box, add an excerpt box to pages and show a jQuery character counter and limiter.

Excerpt character limiter vs Excerpt Tools