Ever been wondered why there's a lot of conflicting advice about longest page title allowed in search results pages (SERPS)?

The short answer is different search engines have different limits and these limits keep changing. The current official guidelines, as of April 2011, are:
  • W3C recommends a maximum of 64 characters for page titles.
  • Bing recommends a title between 5 and 65 characters long.
  • Yahoo recommends a maximum title length of 67 characters (although this advice is obsolete since Bing now supplies Yahoo's search results) 
  • Google don't have any guidance for content publishers, but recommend a maximum title length of approximately 60 characters for Google's own pages.

To see how these play out, we searched for "patent 7143296" in the top three search engines:
  • Bing - titles up to 70 characters are displayed (previously longer titles were truncated to whole words around 53 characters, but this no longer happens)
  • Yahoo - results are now provided by Bing (since mid-2010)
  • Google - titles up to 71 characters are displayed, longer titles are truncated to whole words, with the following exceptions:
    • Results included from Google patent search - patent title is limited to 71 characters but "Google Patent Search" is added to the end of the 71 character title.
    • The title limit used to be 66 characters, and some old documents remain in the index with titles still truncated at 66 characters

This table shows how the maximum title length in the major search engines has changed over time:
YearGoogleBingYahoo
2007 66 chars 65 chars 120 chars
2008 66 chars 65 chars 72 chars
2009 71 chars 65 chars 72 chars
2010 71 chars 67 chars 65 chars
2011 71 chars 70 chars Uses Bing results, so inherits Bing limits
These limits have changed over time, and are likely to keep on changing as the search engines store more pages and optimize retrieval speeds. It's worth noting that the data volumes to store page titles are not trivial. As of Apr 2010 Google had indexed 13 billion web pages, so that's 13 billion page titles to store, with multiple redundant copies needed to provide backup in the event of disk failure.

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Update: Orginally posted April 2010, updated April 2011