As I konw Google truncates your meta description in around 150-155 characters. Yahoo truncates around 145-150. I recommend you to not exceed 150 characters.
if you say about meta description then in from my personal point if view it should be about 150 characters.
It should be 150 characters, but there is no any strict guideline define you can increase it. The main thing is how much characters are visible on search engine matters.
The limit is 160 but you can use upto characters but going above it can hurt your site. Your meta description is visible in the search results if you extend it upto 180 characters than you will not be able to convey your message to the visitor so try to complete your message and purpose of the page in 180 characters.
Ideal character limit in title = 60 - 80, meta-description = 150. Meta-keywords =724 Google shows 69 Characters (Including Spaces) for Page Title. 156 Characters (Including Spaces) for Meta Description. Yahoo shows up to 72 Characters (Including Spaces) for a Page Title. (PDF’s up to 75 characters). 161 Characters (Including Spaces) for Meta Description. Bing shows 65 Characters (Including Spaces) for a Page Title Tag. 150 Characters (Including Spaces) for Meta Description Tag.
When you write 'characters' do you mean spaces included? For instance, if the letters are say, 140 but the total is 175 including spaces, which should be counted.
In Title meta tag - 95 word count with spaces keyword tag - 1000 characters or 45 words Description tag - 50 - 200 characters or 25 words