Count Title and Post Characters

You can use this function wp_strip_all_tags.

strlen( wp_strip_all_tags($post->post_content));

With that you get rid of all the HTML tags.

Just a little extra detail, you might want to strip the shortcodes, too. You can use this function strip_shortcodes

You will end up with something like this:

 strlen( wp_strip_all_tags(strip_shortcodes($post->post_content)));

To convert the encoded entities to the corresponding string value you could use the PHP function html_entity_decode.

Example.

" " </S<>;
is converted to
" " </S<>;

TEST:

//CODE
    var_dump($post->post_content);
    var_dump(wp_strip_all_tags($post->post_content, true));
    var_dump(html_entity_decode(wp_strip_all_tags($post->post_content, true)));
    var_dump(html_entity_decode(strip_shortcodes(wp_strip_all_tags($post->post_content, true))));

 //RESULTS

string 'áé´r´díó' ñ   " " &lt;/S&lt;&gt;;   a

' (length=59)

string 'áé´r´díó' ñ   " " &lt;/S&lt;&gt;;   a ' (length=56)

string 'áé´r´díó' ñ   " " </S<>;   a ' (length=47)

string 'áé´r´díó' ñ   " " </S<>;   a ' (length=38)



//CODE
var_dump(strlen(html_entity_decode(strip_shortcodes(wp_strip_all_tags($post->post_content, true)))));

var_dump(strlen(html_entity_decode(wp_strip_all_tags($post->post_content, true))));

var_dump(strlen(wp_strip_all_tags($post->post_content, true)));

 //RESULTS

int 38
int 47
int 56

As I was using var_dump each string has it’s lenght, but I added the results of the call to the strlen function anyway.