You say

While the U.S. is now converting more than one third of it's corn crop to ethanol,

I have been trying to figure out the correct percentage is myself.

When one looks at this report from the USDA, a person finds the following values:

A. Corn production 13,074 million bushels
B. Food, alchohol and industial use 4,532 million bushels
C. = B / A = 34.7%

I am wondering, however, whether the 4,532 million bushels contains a lot more than ethanol.

If we look at Robert Rapier's post on ethanol, a bushel of corn contains "up to 2.7 gallons of ethanol". If we multiply 2.7 gallons times 4,532 million bushels, we get 12,236 million gallons of ethanol which is way too much ethanol.

If I look at this EIA site, and estimate the month of December, it looks to me like total US produced ethanol for 2007 is going to be something like 6,500 million gallons = 6.5 billion gallons. It may be that there is a year lag, and this year's corn is used to produce next year's ethanol. If that is the case, we are talking about perhaps 9 billion gallons (mandated in 2007 energy bill).

If we use 6.5 billion gallons, that equates to something like 2,407 million bushels, or 18.4% of the 2007 corn crop. If we use 9.0 billion gallons, that equates to 3,333 million bushels, or 27% of the 2007 corn crop. My guess is that is really something in between these two numbers, because there is only a part-year lag, perhaps 25%.

If anyone has any official calculations, I would like to see them.