Calculate estimated corn yield in bushels per acre from ear counts, kernel rows, and kernels per row, with row-length sampling help, moisture adjustment to 15.5%, and total crop value.
Corn Yield Formula
- Y is the estimated corn yield (bushels per acre)
- E is the number of harvestable ears counted in a 1/1000 acre length of row
- K is the average number of kernels per ear
- R is the average number of kernel rows around the ear
- KPR is the average number of kernels per row
- F is the kernels-per-bushel factor (80,000 to 100,000, with 90,000 used for average conditions)
This is the yield component method used by university extension agronomists. You walk to a representative spot in the field, measure off a length of row equal to 1/1000 of an acre, count the harvestable ears in that length, then count kernel rows and kernels per row on every fifth ear to get an average kernels per ear. Multiplying ears by kernels per ear by 1,000 gives kernels per acre, and dividing by the kernels-per-bushel factor converts that count to bushels.
The calculator has three modes. The main mode runs the formula above and can also multiply the per-acre result by your field size and a corn price to show total bushels, total grain weight, and crop value. The row length mode tells you how many feet of row to measure for a 1/1000 acre sample at any row spacing, using L = 522.72 / S, where L is the length in feet and S is the row spacing in inches. The moisture mode converts a measured yield to the 15.5% market standard using:
- Ya is the yield adjusted to 15.5% moisture
- Ym is the measured yield (bushels per acre)
- M is the measured grain moisture (%)
Kernel Weight Factors and U.S. Yield Benchmarks
The kernels-per-bushel factor is the largest source of error in a pre-harvest estimate. Pick it based on grain fill conditions during the season.
| Growing conditions | Kernels per bushel | Effect on estimate |
|---|---|---|
| Excellent, deep heavy kernels | 75,000 to 80,000 | Higher yield estimate |
| Average season | 85,000 to 90,000 | Standard estimate |
| Drought or late-season stress, shallow light kernels | 95,000 to 105,000 | Lower yield estimate |
Use the table below to judge how your estimate compares with national performance. These are USDA national average corn yields, which combine irrigated and dryland acres across all states. A well-managed Corn Belt field on good soil commonly runs 40 to 70 bushels above the national average, so treat the national figure as a floor rather than a target.
| Year | U.S. average yield (bu/acre) |
|---|---|
| 2016 | 174.6 |
| 2018 | 176.4 |
| 2020 | 171.4 |
| 2022 | 173.4 |
| 2023 | 177.3 |
| 2024 | 179.3 |
Corn Yield Estimate Example
Example 1: Yield from ear counts. You farm 30-inch rows, so a 1/1000 acre sample is 17 feet 5 inches of a single row. In that length you count 30 harvestable ears. Counting every fifth ear, you average 16 kernel rows and 35 kernels per row.
- Kernels per ear: 16 x 35 = 560
- Kernels per acre: 30 x 560 x 1,000 = 16,800,000
- Estimated yield: 16,800,000 / 90,000 = 186.7 bu/acre
Example 2: Moisture adjustment. Your yield monitor shows 205 bu/acre at 20.5% grain moisture. Adjusted to the 15.5% standard: 205 x (100 – 20.5) / (100 – 15.5) = 205 x 79.5 / 84.5 = 192.9 bu/acre. Drying removes about 5.9% of the wet weight, so the sellable yield is roughly 12 bushels lower than the monitor reading.
FAQ
When is the best time to estimate corn yield?
Wait until at least the milk stage (R3), and preferably the dough or dent stage (R4 to R5). Before R3, kernel abortion can still reduce kernel counts, which makes early estimates run high. The closer you sample to black layer, the more the kernel counts and kernel weights reflect what the combine will actually harvest.
Why does my estimate differ from the combine yield?
The yield component method fixes kernel weight through the kernels-per-bushel factor, but actual kernel weight depends on late-season rainfall, heat, and hybrid genetics. Sampling bias matters too: counting only good-looking areas inflates the number. Harvest losses from ear drop and header shatter, plus moisture shrink at the elevator, all pull the final number below a field estimate. Expect field estimates to land within about 10 to 20 bushels of actual yield when sampling is done carefully.
How many spots should I sample in a field?
Sample at least 5 locations, and 10 or more in variable fields. Pick spots that represent the whole field, avoid headlands and end rows, and average the ear and kernel counts before running the calculation. If the field has distinct management zones, estimate each zone separately and weight the results by zone acreage.