What this calculator does
The yield component method estimates corn yield before harvest from three numbers: ears in a thousandth of an acre, average kernels per ear, and an assumed kernel size. Multiply the first two, scale up by a thousand, and divide by the kernels-per-bushel factor.
That last factor is where the uncertainty sits. It ranges from about 120,000 kernels per bushel for small kernels down to 80,000 for large, and the choice shifts the estimate by nearly 50%. Since kernel size is not determined until grain fill finishes, estimates made early in the season carry that whole range as uncertainty.
The formula
Ears per thousandth of an acre multiplied by average kernels per ear gives kernels in that sample, and multiplying by 1,000 scales it to a full acre. Dividing by the kernels-per-bushel factor converts to bushels per acre. A thousandth of an acre is about 17 feet 5 inches of row at 30 inch spacing, which is the standard sampling length.
| Term | Meaning |
|---|---|
| Yield component method | The standard pre-harvest estimation approach used by Purdue, Iowa State and other extension services. |
| 1/1000 acre | The sampling unit: 17 feet 5 inches of row at 30 inch row spacing. |
| Kernels per bushel | The size factor: about 90,000 for typical kernels, 120,000 for small and 80,000 for large. |
| Kernels per ear | Rows around the ear multiplied by kernels along a row, averaged across several representative ears. |
The inputs explained
| Field | What to enter |
|---|---|
| Ears counted in a 1/1000-acre sample row | Harvestable ears counted in a thousandth of an acre. Sample several locations and average, since field variability is large. |
| Average kernels per ear | Average kernels per ear, from counting rows around by kernels long on several representative ears. |
| Kernel size factor | Kernel size factor. Use the medium 90,000 unless conditions during grain fill clearly suggest otherwise. |
| Field size (0 to skip total) (acres) | Field size in acres, for a total yield figure. Leave at zero for the per-acre estimate only. |
When to use it
Estimating yield before harvest
Marketing decisions, storage planning and crop insurance discussions all benefit from an estimate made before the combine runs.
Comparing areas within a field
Sampling several spots shows variability directly, which is more useful for management than a single whole-field average.
Assessing damage
After hail, drought or wind, comparing affected and unaffected areas by the same method quantifies the loss.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does ear count change the yield estimate?
A range of ear counts per thousandth of an acre at a fixed kernels-per-ear figure.
| Ears per 1/1000 acre | Estimated yield | Total kernels in sample × 1000 | Kernels-per-bushel factor used |
|---|---|---|---|
| 20 | 111 bu/acre | 10,000,000 | 90,000 |
| 24 | 133 bu/acre | 12,000,000 | 90,000 |
| 28 | 156 bu/acre | 14,000,000 | 90,000 |
| 32 | 178 bu/acre | 16,000,000 | 90,000 |
Questions
How do I measure a thousandth of an acre?
17 feet 5 inches of row at 30 inch row spacing. For other spacings the length changes inversely: 20 feet 10 inches at 25 inch rows, 14 feet 6 inches at 36 inch rows. Measuring the row length wrongly is a straightforward way to bias the whole estimate.
How accurate is the method?
Within roughly 10 to 20% when sampling is adequate and grain fill is complete, which is good enough for planning. Earlier in the season it is considerably less certain, because kernel size is still unknown and late-season stress can still cause kernel abortion.
Which kernel size factor should I use?
90,000 as a default. Use 80,000 if grain fill happened under favourable conditions and kernels look large, and 120,000 after drought or heat stress during fill. Since the factor swings the estimate by nearly half, it is worth being honest rather than optimistic about which applies.
How many locations should I sample?
At least five or six spread across the field, and more if it is variable. Corn fields vary substantially with soil type and drainage, and a single sample taken from a convenient headland is likely to mislead in whichever direction that spot differs.
For heat accumulation through the season, see the growing degree days calculator. For the livestock side, see the feed conversion ratio calculator.