# How do you determine antenna gain from a polar radiation plot?

Using the plot from the Wikipedia Patch antenna page as an example, how is the 9dBi value obtained? It looks like the radiation is barely higher than 0dBi at the strongest location.

• If the blue blob (the plot is a horizontal cross-section of the blob) were a balloon full of water and you would allow it to form a sphere, its outer edge would be at "-9". Is that even right? Sounds about right. :) – AndreKR Aug 16 '13 at 1:58