What gets counted
A word is any group of letters or numbers separated by spaces, so 'well-known' counts as one word and a lone dash counts as none. Characters are counted with and without spaces, because some forms and social sites limit one or the other. Sentences end with a full stop, question mark or exclamation mark, and paragraphs are separated by a blank line.
Reading time assumes an average silent reading speed of about 238 words per minute, and speaking time about 150 words per minute, which is a typical pace for a speech or presentation.
Common limits to aim for
Meta descriptions for search results work best at about 120–155 characters. Personal statements and college essays often have limits around 500–650 words, and many cover letters aim for 250–400 words. Checking as you write saves rewriting later.