How do Smart Banners scale?

I am putting ads into my game at the moment but only have an S3 to test on. Smart Banners fit perfectly on my S3, but I am a little confused as to how they scale. Will they maintain the ratio when I change devices? Like if i change to an iPad, obviosly the screen will be bigger as will the ad, but will it be the same ratio? Or will its height/width look different compared to the S3's ratio. My issue is that ads were an after thought, and i only show them on certain levels due to there only being empty space on some of them. I need the same ratio to happen, otherwise some devices might hide parts of the levels with ads, while some dont.