dr2blog

40 bushels per metric ton times 256280000 Metric tons per year (2023-2024, 390 million metric tons)  times 2.8 gallons per bushel equals about 30 billion gallons of ethanol per year (2023-2024, 44 billion gallons).

divided by 385 million gallons per day equals 78 days (2023, 376 million gallons per day, or 116 days).

Extra credit: multiply the ethanol production by the ratio between the energy of ethanol and the energy of gasoline.

But (that link is dead, but similar content here)

Will we deplete human and animal food supplies by using corn and other grains for fuel production?

No, actually the production of ethanol from corn uses only the starch of the corn kernel, all of the valuable protein, minerals and nutrients remain. One bushel of corn produces about 2.7 gallons of ethanol AND 11.4 pounds of gluten feed (20% protein) AND 3 pounds of gluten meal (60% protein) AND 1.6 pounds of corn oil.

And actually distillers grains make tasty crackers (I have eaten some, and will eat more as long as they are in business).