Apple does not provide any way to count the number of characters in a selected text. Fortunately, you can create your own very easily using Automator.
Launch Automator and create a new Service. Add the Run AppleScript script action, then paste the following code:
on run {input, parameters}
try
set MyText to input as string
set NombreSignes to the number of characters of MyText
set NombreMots to the number of words of MyText
set NombrePara to the number of paragraphs of MyText
set LeResultat to "The selected text contains :" & return & "- " & NombreSignes & " sign(s) ;" & return & "- " & NombreMots & " word(s) ;" & return & "- " & NombrePara & " paragraph(s)."
display dialog LeResultat buttons {"OK"} default button 1 with icon note
on error errmsg number errnum
display dialog errmsg & " [" & errnum & "]" buttons {"OK"} default button 1 with icon stop
end try
return input
end run
Mac OS X Hints
http://hints.macworld.com/article.php?story=20120428125918199