Corn Yield Calculator
The kernel-weight factor alone swings the estimate by forty percent, which is why it is quoted as a range.
The formula
bushels per acre = ears per acre * kernels per ear / 90,000
Counting a crop before it is cut
The yield component method estimates maize yield from three things you can count in the field: how many ears are standing, how many kernels each carries, and how many kernels make a bushel. The first two are counted; the third is the estimate, and it is where the uncertainty lives.
The kernel-weight factor
Ninety thousand kernels per bushel is the average-season figure. A good finish with plenty of moisture fills kernels heavier and the number drops towards 75,000; a hot dry August leaves them light and it climbs past 105,000. Since it divides the whole estimate, that range alone moves the answer by 40 % — which is why the method is run with three factors and quoted as a range.
Count more than you think you need
Ear counts vary enormously across a field. A single sample tells you about that spot and very little about the field, and the usual advice is at least five widely separated samples. The arithmetic below is exact; the sampling is what determines whether the answer means anything.
Rules of thumb, and the field
Every figure here describes an average season on an average site. Soil type, aspect, drainage, variety and weather each move the answer by more than the arithmetic does, and a grower who has kept records for a few years on one piece of ground knows it better than any formula. Use these to plan an order or size an implement, then trust what the ground has actually done before.