1. It varies by query type (some are navigational, research-driven or transactional) and nobody but the engines know for sure, but most people seem to agree that 70-80% of the clicks on a SERP are on the organic results, the other 20-30% are on sponsored results. Additionally, 90%+ of searchers don’t look past the first couple pages of search results, or even past the top 5-7 results for that matter (more here, here, and here (PDF)). So we can guestimate that roughly 50% of the clicks on a SERP are going to occur on the top 3-5 results and beneath that you are just fighting for scraps. PPC results are even easier to estimate, just run a test campaign and rotate your ads at various positions to see the differences in CTR. Divide that by your share of voice and you get a pretty reasonable estimate of the PPC traffic potential.

2. That’s where it pays to be focused on conversions, not just top-level traffic. Even if you only get some long-tail traffic in different keyword segments, you should be able to compare your conversion rates to other segments and figure out where to focus your SEO or PPC efforts. And, if there are popular keywords out there that you are missing out on completely, chances are your keyword research would uncover them and you can run a quick PPC test to determine if they are worth optimizing for or not.

Hope that helps.

Well done! I have a couple of follow-ups.

1. Regarding the last two paragraphs of your post, is there any guidance as to what percentage of the average search traffic you would get if either optimizing for or bidding on particular keywords? For example, could I reasonably say I’d capture 1-2% of the traffic for a keyword if I were to achieve first page results or a reasonable PPC campaign?

2. If I were to only look at Google Analytics for keywords that I’m already getting a low amount of traffic from, aren’t I missing popular terms that I might not be optimized for?

Love your methodology, by the way!