By contributor Lynn Truong
The Rank Number determines your ad position. The higher the Rank Number, the higher your ad will show. It is calculated by multiplying your maximum CPC bid and Quality Score. This means that if you have a low Quality Score, you can still raise your Rank Number by placing a higher bid. Through this system, Google rewards high performing ads with low CPC rates, and makes low performing ads cost more for the same ad position.
The Rank Number is calculated for each keyword individually, and recalculated every time a search is performed. Google's Traffic Estimator tool in your campaign management tab will give you an estimate of what position your ads are likely to appear.