Google announced on Wednesday that it is launching responsive ad units for AdSense in beta. The units enable publishers to support multiple devices with responsive design web pages by letting them specify the size of the ad that will be served.

Publishers can simply create the unit, then modify the sample CSS media queries in the new ad code.

“Be sure to specify fixed pixel values when setting the width and height of the ad to be served,” notes AdSense product manager Nick Radicevic. “Make sure that the specified width and height match one of our supported ad sizes. Please note that link unit sizes aren’t supported at the moment.”

“The new ad code is responsive on initial page load only,” Radicevic adds. “Subsequent changes to the ad size, such as a screen orientation change, will not cause a new ad to be displayed. We know that this is an important feature for many of you and we’re currently working to address this.”

Google has more details about creating the responsive ad units, along with some examples in its help center.