In-feed ads are responsive ads which means they automatically adjust their size for the device they're being viewed on. The width of an In-feed ad is always equal to the width of the feed container it's inside. (Note that the minimum width for an In-feed ad is 250px.) The height of an In-feed ad is automatically adjusted by AdSense to ensure that all of the ad's elements fit well in the available space.
In-feed ad settings and In-feed responsive behavior
To ensure that your In-feed ad appears the way you want it to, it's important to understand how the responsive behavior of In-feed ads affects In-feed ad settings.
Padding is not responsive. Any padding that you set around the top, bottom or sides of your ad will remain the same across all screen sizes.
If you specify image size as a percentage, then the image will change size across different sized screens. However, if you specify image size in pixels, then the image will keep the same size across all screen sizes.
Font size is not responsive. Any font sizes that you set will remain the same across all screen sizes.
If you want the text in your ad to wrap around the image if the screen size changes, you can turn on the Text wrap setting.