Google announced a new Advertisement unit which will help you to match the advertisement with your ad space on December 11.
Custom sized ad units may have a limited inventory of display ads available, which could have a negative impact on your earnings. If your site uses responsive design, we recommend that you use a responsive ad unit instead.
Google will display ads of smaller size on a custom ad size unit, that is if you placed a 400x300 ad unit on your website Google may be showing a 300x250 or 335x280 ad units on that. The smaller ads will be displayed on the center of the unit.
Only one dimension can be greater than 300 pixels
The minimum width is 120 pixels
The minimum height is 50 pixels
Neither height nor width can exceed 1200 pixels.
Next question will be should I use it or to stick with existing ad units ? There is no straight answer for this question. It depends, for some users existing one may be good and for some others this new unit may be good.
How to find – answer is try and find. change to the custom ad size for at least one week and compare it with previous units earnings and decide. When you compare them you must consider the traffic you received during that time.
For unique ad unit sizes, our system will need some time before it can optimize the number of ads shown
So if the earning of a unit do not have much variation from your previous unit, we will prefer you to keep at least for a month and see the difference.
[Inside AdSense – link]