Google announced a new ad size for AdSense today: the 300X600.

“As screens grow and web content continues to become richer, the format and capabilities of ad units continue to evolve as well,” says AdSense UI engineer Omer Gimenez Llach, adding that one of the top requests from publishers has been for larger ad sizes.

“The 300×600 unit, sometimes referred to as a half page unit, provides a larger space for advertisers to get their message across and can offer users rich engagement,” he adds. “As mentioned in our recently released Display Business Trends, the 300×600 is one of the fastest growing sizes by impressions and is indicative of a trend where publishers are offering more visually impactful ad sizes that are preferred by brand advertisers. Because this unit is new to our network, you’ll currently see a large number of text ads in these placements. Over time we’ll continue to build a wide range of text and display ad inventory eligible to appear in this full slot as well.”

Google has guidelines for ad placement here (you know how they feel about having too many above the fold).

The unit will be available in AdSense accounts soon, but the exact time has not been specified.