One of the most common ways to estimate corn grain yield is to first count the number of harvestable ears per 1/1000th of an acre. Next, count the number of kernel rows per ear on every fifth ear, and figure the average. Then, count the number of kernels per row on these ears, and figure the average. Finally, figure yield in bushels per acre as (ear #) x (average row #) x (average kernel #) / 90.
If the year has been unusually dry and the kernels are small, then use 110 instead of 90 in the equation.
Row length needed to equal 1/1000th of an acre in 30-inch rows is 17 feet 5 inches. For 20-inch rows, the row length is 26 feet 2 inches. For 36-inch rows, the row length needed is 14 feet 6 inches.
For a lengthier discussion on estimating corn grain yields prior to harvest, see the following Web-based article from Purdue University:
www.kingcorn.org/news/timeless/YldEstMethod.html
