letter in meta title and meta description

is there any rule for number of letters or words on meta title and meta description? if yes then how many and why?

i hope to get correct answers.

thanks

 

Well, this what the google contributor to a google group had to say about meta descriptions , so I guess that's correct
http://groups.google.com/group/Google_Webmaster_Help-Indexing/browse_thread/thread/7c5dc8cbb5f07dcd

There's no fixed number of words/characters that you're "allowed."

For the title, 66 characters are shown

 

A good rule of thumb to follow is 60 characters title, 150 for description. A few more or less may be shown, but those numbers should assure getting your content picked up as you want it in Google.

 

60 characters title, 150 for description...is better