I want to know why meta tag title should be less than 70 char? can anyone please tell me exact answer for this as soon as possible?
Simply because anything longer than that is unlikely to be displayed, either by the browser or in search results. There’s a useful article here about titles:
actually seo site that I use recommends using up to 65 char however I could swear I saw somewhere that that you can have up 75 char.
anyhow for the reason TechnoBear mention above I would suggest for you to exceed 75 char or even try to keep it under 70.
As explained by others if your title goes more than 70-80 characters, it wont be visible to readers. Google want you to make site more user friendly. if reader could not make sense out of your websites title, it will be called bad title. you can refer one tool which will help you to see how your title will look in google. http://www.seomofo.com/snippet-optimizer.html
You should really try to forget about SEO and Google when considering this sort of question. The only thing that really matters is choosing a title that best conveys to your visitor what the page is about - and encourages the visitor to read it. This isn’t easy. The best titles are often the shortest ones, but don’t get bogged down in worrying whether 65 characters is better than 70, or 70 better than 75.
And for goodness sake don’t make it harder for yourself by obsessing with what Google will think of your title. It’s what the humans think that counts.
Mike
I think you will find that the original standard for this tag specified that browsers are allowed to discard anything beyond the first 65 characters. I don’t know if that has been changed since but there would be little reason for it.
I did my research about this when I reviewed our on-page seo strategies. Meta tags have limits as we all know that. But in the recent months, I read that it’s not about the number of characters. It’s the pixel measurement of the the characters used. You can find a couple of free pixel meters online that would help you write Title tags that would fit the search engines, particularly Google.
But as @Mikl has already pointed out, you should be writing your title tags - like the rest of your site, primarily for your human visitors. If it works for them, it will work for search engines.
I’m pretty sure nobody buys a car by studying the size of their garage, choosing one to fit and then hoping it will also meet the needs of their family. They consider the family requirements first. So why so many folk choose to do things back-to-front when it comes to websites and SEO is beyond me. 
I have found many titles which are more than 70 characters and many are less than 70 characters. Better to use tool before implement on site. Here below I have mentioned link which help you to optimize your title: http://moz.com/learn/seo/title-tag
You can make the title as long as you like. Browsers etc are allowed to ignore everything past the first 65 characters and search engines know that so whatever you put in position 66 in the string will almost certainly be ignored - as will anything after that as they are no longer a part of the title but simply random noise added between the end of the title and the closing tag for the title.
<title>tttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttnnnnnnnnnnnnnnn</title>
has a title of ttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttt and is identically equivalent to writing
<title>ttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttt</title>
browsers might optionally include one or more of the ‘n’ characters from that string but if they do so they are ignoring the standards.
If anyone really needs a tool to judge whether their title is a suitable length, I would question whether they are in the right business.
As we’ve already said several times in this thread, you should write your titles for humans. If you don’t know how to do that, either hire someone who can, or use your talents elsewhere.
Mike
And that seems to sum things up nicely.
The question has been well answered, and the OP has never returned.
Thread closed.