PPC or pay per click uses Google Adwords as a means of generating advertising and marketing results, in an affiliate marketing context this means that affiliates use their affiliate link as their directory URL, this means that whilst Google can track the impressions and clicks, the affiliate link tracks the conversions on the merchant site. Whilst the affiliate will have to pay Google for each click, the theory is that the commission earned from actual conversions will compensate the cost of clicks. To support this one of the UKs  well known affiliates has created a tool to help affiliates calculate the numbers involved in PPC, the idea is with these numbers an affiliate can predict how profitable an affiliate program will be using PPC.

Check out the PPC calculator here.