// In Functions.php:
function the_excerpt_max_charlength($charlength) {
   $excerpt = get_the_excerpt();
   $charlength++;
   if(strlen($excerpt)>$charlength) {
	   $subex = substr($excerpt,0,$charlength-5);
	   $exwords = explode(" ",$subex);
	   $excut = -(strlen($exwords[count($exwords)-1]));
	   if($excut<0) {
			echo substr($subex,0,$excut);
	   } else {
			echo $subex;
	   }
	   echo "[...]";
   } else {
	   echo $excerpt;
   }
}




// In wordpress template:
<?php the_excerpt_max_charlength(250); ?>

http://codex.wordpress.org/Function_Reference/get_the_excerpt

function that creates a template tag that can be used to insert excerpts with different lengths. Also controls characters that come after excerpt

Wordpress excerpt length tag

wordpress

PHP