There is an additional 47 million acres in conservation programs. We actually have about 1,000,000,000 acres of useful farmland.
About 20% of the world’s farmland. The only way to understand the full size of this is to drive from Southern Kansas to Northern Nebraska and try to find a human in the corn and wheat.
I was watching Modern Marvels on the History Channel about corn and they stated that the American farmer produces enough corn to supply every human on the planet with around 120 pounds of corn per year.