How Reliable Is Google’s “site:domain.com” Query?

Matt Cutts from Google is back with a new video post about Google’s site: query.

The site: query can be used by anyone to determine how many of a given site’s pages have been crawled and indexed by Google. Simply type “site:domain.com” (minus the quotes) into the Google search field. It will return a list of all of the pages Google has indexed from the domain. Though, as Matt points out in this clip, it’s not as accurate as you might hope.

Matt says – “Site colon queries attempt to estimate how many pages are in our index”. You wouldn’t think that a database would need to “estimate”, but apparently this one does. Matt goes on to tell us that a site: query will only ever return “three significant digits of precision” and will always include “About”. So, that could be About 691, or About 179,000,000, and they’re not going to make any claims about the accuracy of either one.

This isn’t fantastically useful information from an SEO perspective, but it does indicate that Google’s ability to handle million page sites in their database isn’t as flawless as you might have imagined.