Earnings: One Ad Unit vs Many

Adeel asks:
I have heard if we have only one Ad in our blog we earn more per click. Is it true??


Answer:
This is a tricky question so I thought of posting it separately from the question with which it was asked with. Hope the answer is tricky too ;)

Google Adsense shows the ads with maximum earning potential on the ad space that you provide on your site. When I say earning potential, I do not mean earnings per click.

Total Earnings = no. of clicks x Cost per click

For some ads, the number of clicks (CTR) may be high and Cost per click (CPC) may be low but still can manage to have a high earning. For some other ads, the CTR may be low and the CPC may be high but still won’t have high earnings! Now Google brings up ads that will deliver you the maximum earnings.

Now into the question, let’s take this case. You are having a long page, requiring users to scroll down the page. Now it will be always better to have ads at both ends of the text. Another example is a Forum or message board pages. It’s better to have ads between posts. All this requires you to have multiple ad units to gain maximum visibility.

Google advices to place the ad that appears first in your HTML code in the most visible position so that they can deliver the ads with maximum earning potential to it.

So in effect if (that is a big if) you can manage to place a single ad unit that is visible enough such that you have a healthy CTR, you will have a higher earnings.
Again, remember that placing 2-3 ad units will have a better chance to be visible!