The longest page title that I would use is 67 characters, many use a 60 character limit, some use 64, and some 128.
I’ve read different opinions on webmaster and seo forums (like 64 character limit and truncate to 64 if longer than 70), but seen with my own eyes that the page title on a serp can be up to 70 characters, this is including the … that is added, so that leaves 67 characters as the max, but only if your word boundary falls at the 67th character! huh?…read on for more.
Google truncates (and may not index) anything over 67 characters (including spaces) if you have a page title over 70 characters, based upon what I’ve seen. Looks to me like the length varies because the truncation is to the next shortest whole word. Amazingly, I’ve not actually read or heard this, so try it for yourself if you want to believe it. Just search for whatever and use a text editor to count characters on the longest titles returned on the search results page.
The truncated part (the tailing part is clipped off and discarded) may not even be indexed! I am not sure of this, but have a personal policy of not deliberately using anything over 67 characters to describe my page.
Also a longer page title “dilutes” the keyword weighting of those that are in the title, so if you use a long title with lots of words the ones you do use will have less importance to the search engine.
About 6 to 7 words is a good working objective.