Corn Yield Calculator (yield component method, bu/acre & t/ha)

Understanding the corn yield estimate calculator — concept and principle

Before harvest, farmers and agronomists often estimate corn yield with the yield component method: count ears in a measured length of row and kernels on typical ears. This calculator turns those counts into bushels per acre and tonnes per hectare.

Ears per acre × kernels per ear gives total kernels; dividing by 85,000 kernels per bushel gives about 187 bu/acre.

How it is calculated

Ears per acre = ears counted ÷ (row length × row spacing) × 43,560 ft².
Kernels per ear = kernel rows × kernels per row.
Yield (bu/acre) = ears per acre × kernels per ear ÷ kernels per bushel.
t/ha = bu/acre × 56 lb × 0.45359237 kg/lb ÷ 0.40468564 ha/acre ÷ 1,000.
Row length for 1/1,000 acre = 43.56 ÷ row spacing in feet.

The principle

Yield is the product of plants (ears) per area, kernels per ear and kernel weight. The first two can be counted in the field before harvest; kernel weight cannot, so the method assumes a number of kernels per 56-lb bushel at 15% moisture. Large kernels mean fewer per bushel and higher yield for the same count, which is why that assumption is the biggest source of error.

Worked example

Default inputs: 30-inch rows, 17.4 ft counted, 31 ears, 16 kernel rows, 32 kernels per row, 85,000 kernels per bushel.

Row length for 1/1,000 acre at 30-inch rows = 43.56 ÷ 2.5 ≈ 17.4 ft.
Ears per acre = 31 ÷ (17.4 × 2.5) × 43,560 ≈ 31,043 (76,708 per hectare).
Kernels per ear = 16 × 32 = 512.
Yield = 31,043 × 512 ÷ 85,000 ≈ 187 bu/acre.
In metric ≈ 11.74 t/ha at 15% moisture.

Each point is the calculator re-run with only “Row spacing” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Row spacing	Estimated yield (bu/acre)
7.5	747.9
15	374
22.5	249.3
30	187
37.5	149.6
45	124.7
60	93.5

How to read the result

Try kernels per bushel of 65,000, 75,000 and 85,000 to see the range; in a stress year with small kernels, the higher number fits better. Sample several spots across the field, because one sample rarely represents the whole field. Compare the estimate with combine yield monitor data after harvest to calibrate your assumptions.

Common mistakes

Counting ears that will not be harvestable (very small or barren ears).
Using the wrong row spacing.
Sampling only the best or worst part of the field.
Treating the estimate as precise; errors of 10–20% are common.

Keep in mind: Pre-harvest estimates are rough. Use them for planning, not for contracts or insurance claims.

Frequently asked questions

How do you estimate corn yield before harvest?

Count ears in 1/1,000 acre of row, multiply by kernels per ear and divide by kernels per bushel (in thousands).

How many kernels are in a bushel of corn?

Roughly 65,000–90,000 depending on kernel size.

Why is the estimate often off?

Kernel weight is unknown before harvest and field variability is large.

Sources: Nielsen, R. L. (Purdue University Agronomy), Estimating Corn Grain Yield Prior to Harvest · USDA Agricultural Marketing Service, standard test weight of a bushel of corn (56 lb)

Checked 9 Nov 2026. Nielsen R.L. (Bob), “Estimating Corn Grain Yield Prior to Harvest”, Purdue University Agronomy Dept., Corny News Network, revised August 2021: yield (bu/acre) = ears in 1/1000 acre × kernels per ear ÷ kernel factor; factor 90 (90,000 kernels per 56-lb bushel at 15% moisture), 65–85 suggested, 90–100 after stress.

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