Google’s AdWords keyword tool gives an estimate of search traffic for a specific (or broad) keyword. In a recent video from Matt Cutts on the GoogleWebmasterHelp YouTube channel, Matt explains that the far majority of traffic to most websites is natural.

Matt explains that Google does a good job of stripping out “artificial” traffic from bots. The longer your keyword phrases are (i.e. the more words in your targeted keyword phrase) the more accurate and organic the traffic statistics will be. So, unless you are searching for very spammy keyword phrases (like “search engine optimization”) your traffic estimates in Google’s Adwords keyword tool will be pretty close to actual.