Corn Yield Calculation Example

Let's walk through a real yield estimate on a hypothetical 160-acre field of corn-after-soybeans in central Iowa. It's the last week of August, the crop is at R5 (dent), and we want a number to use for forward contracting and storage planning. The goal is to turn a 20-minute field walk into a bushels-per-acre estimate with an honest plus-or-minus range.

Our field has 30-inch rows planted at 34,000 seeds per acre. The hybrid is a 111-day relative maturity that typically produces 16 kernel rows. Pollination in mid-July was clean — warm but not extreme, with adequate soil moisture. August was slightly drier than normal but no serious stress. Based on the five-year average plus 5%, our yield goal going into the season was 200 bu/ac.

Before sampling, we split the field into four rough zones based on what we know about it:

• Zone A (north half): Flanagan silt loam, well-drained, consistently the best part of the field.
• Zone B (southwest quarter): Slightly heavier Drummer silty clay loam, holds water in wet years.
• Zone C (southeast quarter): Lighter Tama silt loam, dries out faster in summer.
• Zone D (field edges): Skip these — border rows and headlands don't represent the field.

We'll take two samples in Zone A, one in Zone B, and two in Zone C — five samples total, weighted toward the larger zones. We avoid the field edges, the low spot near the creek, and the old fence line where the soil changes.

At each sample location, we lay out 17 feet 5 inches of row (1/1000 acre for 30-inch rows), count harvestable ears, and pull one ear to break open and count kernel rows and kernels per row. Here are the five samples:

Now average each column across the five samples:

• Average ears per 1/1000 acre: (34 + 33 + 32 + 30 + 31) ÷ 5 = 32.0 → 32,000 ears per acre
• Average rows per ear: (16 + 16 + 18 + 16 + 16) ÷ 5 = 16.4 → 16 rows (round to typical hybrid count)
• Average kernels per row: (38 + 36 + 40 + 34 + 36) ÷ 5 = 36.8 → 37 kernels per row

Note the variability: ears range from 30 to 34 (a normal spread), rows from 16 to 18 (one ear in Zone B had 18 — the hybrid is mostly 16), and kernels per row from 34 to 40 (Zone C is slightly lower, reflecting the drier soil). The averaging smooths out this variability into a single representative set of numbers.

At each sample we shell a handful of grain and test moisture. The five readings are: 24%, 25%, 26%, 25%, 24%. Average: 24.8%, round to 25%. This is a typical moisture for central Iowa corn at R5 in late August — the crop has dented but hasn't dropped much below 25% yet.

Now plug the averaged numbers into the formula:

Yield = (Ears × Rows × Kernels) ÷ 90,000 × [(100 − Moisture) ÷ 84.5]

1. Total kernels per acre = 32,000 × 16 × 37 = 18,944,000
2. Raw yield = 18,944,000 ÷ 90,000 = 210.5 bu/ac
3. Moisture factor = (100 − 25) ÷ 84.5 = 75 ÷ 84.5 = 0.888
4. Adjusted yield = 210.5 × 0.888 = 186.9 bu/ac

Our yield estimate is 187 bushels per acre at standard moisture. With a 5-sample protocol, the honest accuracy range is plus or minus 10%, so the honest estimate is "somewhere between 168 and 206 bu/ac." For forward contracting we'd use the low end (168); for storage planning we'd use the midpoint (187).

Before acting on the estimate, run a few sanity checks:

• Is the yield in a realistic range for the field and year? The five-year average was ~190, our yield goal was 200, and August was slightly dry. An estimate of 187 is right in line — no red flags.
• Does the ear count match the planting rate? We planted 34,000 seeds/ac with ~95% survival, expecting ~32,000 final stand. The ear count of 32,000 matches — no obvious barrenness or stand loss.
• Are the kernel counts reasonable? 16 rows is typical for this hybrid; 37 kernels per row is in the normal 30-40 range. No sign of major pollination problems.

If the estimate had come back at 150 or 240, those sanity checks would flag a problem — either a sampling error or a real issue in the field. In this case, 187 passes all three checks, so we can use it with reasonable confidence.

The final estimate: 187 bu/ac, plus or minus 19 (range: 168 to 206). On 160 acres, that's 29,920 bushels at the midpoint, with a range of 26,880 to 32,960. We can now:

• Forward-contract up to ~27,000 bushels (the low end) with reasonable confidence
• Line up ~30,000 bushels of storage at the elevator or in on-farm bins
• Schedule ~75 truckloads (at 400 bu/truck) over a 5-7 day harvest window
• Compare to the yield goal of 200 and start diagnosing the 13-bushel gap for next season

One 20-minute field walk, five samples, and a few minutes of arithmetic turned a guess into a planning number. That's the value of the USDA ear count method — and you can run the same process on your own field with the calculator on this site.