Corn Yield Calculator
Enter four field measurements and get an instant, moisture-adjusted bushels-per-acre estimate using the USDA Yield Component Method.
Enter Your Field Measurements
All four values come from a quick field walk — no equipment needed
Count in 17'5" of 30" row × 1000
Count around the ear, avg of 5
Base to tip, avg of 5 ears
Use a moisture tester; standard 15.5%
Use "Average of multiple" for best accuracy
Walk at least five spots in the field. At each, count ears in 1/1000 acre (17'5" of 30" row) and pull one representative ear. Average everything at the end. Five samples cut your error roughly in half compared to one.
Yield = (Ears × Rows × Kernels) ÷ 90,000 × moisture factor. The 90,000 comes from the long-run average kernels per bushel at 15.5% moisture — a USDA figure used since the 1960s.
How This Calculator Works
This corn yield calculator runs the USDA Yield Component Method end to end. The method breaks a corn crop into three countable pieces — ears per acre, kernel rows per ear, and kernels per row — multiplies them to get total kernels per acre, then divides by 90,000 to convert kernels into bushels. The 90,000 divisor is the long-run average number of kernels needed to fill one bushel of #2 yellow corn at 15.5% moisture, and it comes straight from USDA and land-grant university extension literature rather than an internal guess.
After the raw bushel figure is computed, the calculator applies a moisture adjustment. Corn is bought and sold at 15.5% moisture, so if your grain is wetter (say 22% at black layer) the raw weight overstates saleable bushels, and if it's drier (say 13% after a dry down) the raw weight understates them. The adjustment factor is simply (100 − your moisture) ÷ (100 − 15.5), which scales the yield up or down to what the grain would weigh at the standard. Enter the moisture your tester reads and the math handles the rest.
The Full Formula
Adjusted Yield (bu/ac) = (Ears × Rows × Kernels) ÷ 90,000 × [(100 − Moisture) ÷ 84.5]
What Each Input Means
Ears per acre is the count of harvestable ears — ears with at least a few hundred kernels — across one acre. You get it by counting ears in 1/1000th of an acre and multiplying by 1,000. For 30-inch rows, 1/1000 acre is 17 feet 5 inches of row. For other row widths the length changes, but the 1/1000 logic stays the same.
Rows per ear is the number of kernel rows running around the cob. It's almost always an even number (14, 16, or 18) because rows develop in pairs. This trait is set by genetics, so within a hybrid it's quite stable — usually a sign of trouble if it's lower than the hybrid's typical count.
Kernels per row is the number of kernels running lengthwise from base to tip. This is the most variable of the three: it reflects how well pollination went and how much grain fill happened. Stress during silking (mid-July in the Corn Belt) directly cuts this number.
Grain moisture is the percent water in the grain at the time you're estimating. Use a handheld moisture tester on a shelled sample. If you don't have one handy at R5/R6, 25-35% is typical — but guessing here adds error, so test if you can.
A Worked Example
Suppose you walk a central Iowa field in late August and find the following at five sample locations. Each location gives you an ear count (in 1/1000 acre) plus one ear to break open.
- Sample 1: 33 ears, 16 rows, 38 kernels/row
- Sample 2: 31 ears, 16 rows, 36 kernels/row
- Sample 3: 34 ears, 18 rows, 40 kernels/row
- Sample 4: 30 ears, 16 rows, 34 kernels/row
- Sample 5: 32 ears, 16 rows, 38 kernels/row
Averaging: ears = (33+31+34+30+32) × 1000 = 32,000 ears/acre. Rows = (16+16+18+16+16)/5 = 16.4, round to 16. Kernels/row = (38+36+40+34+38)/5 = 37.2, round to 37. Moisture reads 28%.
Raw yield = (32,000 × 16 × 37) ÷ 90,000 = 18,944,000 ÷ 90,000 = 210.5 bu/ac. Moisture factor = (100 − 28) ÷ 84.5 = 72 ÷ 84.5 = 0.852. Adjusted yield = 210.5 × 0.852 = 179.3 bu/ac — right at the US national average. Plug the same four numbers into the calculator above and you'll get the same result.
Frequently Asked Questions
Everything you need to know
Yes, completely free. There's no sign-up, no email wall, and no limit on how many times you can run a calculation. The site is supported by advertising, which keeps the tool free for everyone.
You need a tape measure (to lay out 1/1000 acre), a way to count ears, and ideally a handheld grain moisture tester. If you don't have a moisture tester, you can estimate 25-35% at R5/R6 stage, but a real measurement makes the result meaningfully more accurate.
A yield monitor measures flow during harvest and gives you a final number after the crop is in. This calculator gives you a planning estimate weeks earlier, while the crop is still standing. The two complement each other: use this one to plan, use the monitor to verify.
90,000 is the long-run average number of kernels required to make one bushel of #2 yellow corn at 15.5% moisture. It's a USDA and extension standard used since the 1960s. In a high-test-weight year the real number might be closer to 80,000; in a low-test-weight year it might be 100,000. The 90,000 figure is the middle-of-the-road default.
Editorial Standards & Sources
All formulas and benchmarks on this page are based on the USDA Yield Component Method (Nielsen, R.L., Purdue University Extension) and USDA NASS crop production data. Our calculators are reviewed annually against the latest extension publications from Iowa State, University of Illinois, University of Nebraska, and Ohio State.
Methodology: The default 90,000-kernels-per-bushel divisor and the 15.5% moisture standard used throughout this site come directly from published USDA and land-grant extension guidance rather than an internal estimate. Where a figure is our own approximation — such as the ±10% accuracy range for the ear count method — we say so explicitly rather than presenting it as an official statistic.
Known limitations: Pre-harvest estimates from any ear-count-based calculator are a planning tool, not a substitute for actual combine yield-monitor data or elevator scale tickets. Accuracy depends heavily on how representative the field samples are; we recommend a minimum of five sample locations per field, as outlined in the sampling guidance on this page.
Content last reviewed for accuracy in August 2025. Have a correction or suggestion? Contact our editorial team — we respond to all substantive feedback within 5 business days.