What is the area of a billboard?

In North America, "bulletins" are typically 14'x 48' = 672 square feet (on one face), but they are smaller in other places.

Currently, four states-Vermont, Alaska, Hawaii, and Maine-have prohibited billboards.

Billboards come in a variety of sizes. Common sizes are 10'x24', 12'x24', 14'x48', and 16x60.

The linked articles may help.