To estimate the crop yield, producers usually count the amount of a given crop harvested in a sample area. The harvested crop is then weighed, and the crop yield of the entire field is extrapolated from the sample.
For example, if a wheat producer counted 30 heads per foot squared, and each head contained 24 seeds, and assuming a 1,000 kernel weight of 35 grams, the crop yield estimate using the standard formula would be: 30 X 24 X 35 X 0.04356 = 1097 kg/acre. And since wheat is 27.215 kg/bu, the yield we estimated would be 40 bu/ac (1097/27.215).