Using this text:
Code:
<div>
<p>Prevod: ˇivković Mirjana; Naslov originala: Anderson Poul THREE HEARTS AND THREE LIONS, 1961.</p>
<p>Prevod: ˇivković Mirjana; Naslov originala: Anderson Poul THREE HEARTS AND THREE LIONS, 1961.</p></div>
and using the template {comments:strlen()}, I get 213 characters.
If I manually count the displayed characters I also get 213, the same as the template. Don't forget that the end of line is a character.
Loading that text into Notepad++, a text editor, I get 217 characters. The difference between Notepad++ and the template is that Notepad is counting the components (bytes) of composed characters, for example ˇ and ć, as two characters (bytes). There are 4 such characters in the string, making the length 4 longer: 217 instead of 213.
I have no idea where the 188 comes from. Nor do I know where the "online tool" gets 211.
In any event, the output of the template is the best count your going to get from calibre.