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How precise is the number of results in a site: query?

How precise is the number of results in a site: query? - answered by Matt Cutts

Matt's answer:

Matt: We have a question from Blind Five Year Old in San Francisco. Who asks,” How reliable is the ‘site:domain.com’ query in determining the number of pages in the Google index?” Fantastic question and let me share a little bit of trivia that not many people realize. “Site:” queries attempt to estimate how many pages are in our index, but we would never claim that it is an exact amount that’s completely accurate. In fact, let me just do a couple of queries and mention the number of results: “site:yahoo.com” returns 138 million results. It says about 138 million results. “Site:microsoft.com” returns about 8,250,000 results. Now the thing to notice, between these two, is in both cases we’re only given three significant digits of precision. It turns out any time you do “site:” queries, we only give three significant digits of precision. We wanted to give people the idea of how many results there were, and it is a relatively good estimate, but we didn’t want to claim- this is the exact number of pages that we have indexed. It turns out that once you get passed a few thousand pages that’s not all that useful as a metric. A lot more of the time people should care about how much traffic they get to which pages, the return on investment, the conversion rates, all that sort of stuff; rather than, just the raw number of pages that gets indexed, or even the raw number of pages that get indexed from your site map or xml site map, stuff like that. So, because of that even from the earliest days that I can remember at Google, we only return three significant digits for the “site:” query. So, if you want to impress fellow SEOs who haven’t watched this video, you can sort of wow them with that, ’cause a lot of people haven’t ever noticed that. But it’s just a small fact to show the-to show the, you know, fact that “yes” we do have a pretty good estimate, but “no” it’s not perfect. We know it’s not perfect, and rather than put a ton of engineering resources into making “site:” queries incredibly accurate, we send those engine– spin those engineering cycles on other stuff and then show only the three significant digits so the people have an idea of the total amount of pages, but that it’s not exact. Hope that helps.

by Matt Cutts - Google's Head of Search Quality Team


Original video: