Pre-Harvest Field Estimation
Corn & Soybean
Yield Estimator
Estimate yield from field counts at R5–R6 (corn) or R6–R7 (soybeans) — the same ear-count and kernel-count math crop tour scouts run in August. Pod-count method for soybeans. Sample at least 3 locations per field for reliable estimates. Then see what the trade expects the national number to be.
Method: Yield Component Method (Nafziger, University of Illinois; widely referenced across US Corn Belt extension services).
Accuracy: corn estimates run about ±20 bu/ac — the figure Purdue, Iowa State, Ohio State and Penn State Extension all give for this method. Sample at least 5 locations, 10 ears each, and estimate at the milk (R3) stage or later. Soybean estimates are looser still; Michigan State puts them at ±25% or worse before R6.
Not a substitute for certified yield monitoring or combine data.
Corn Yield Estimator
Ear Count Method Quick Fill — Start from a Typical Scenario
Select a scenario to auto-fill inputs:
Step 1 — Count Ears
Sets 1/1000-acre row length
Row length: 17'5" · typical 28–36 ears
Step 2 — Count Kernels (5 Representative Ears)
Count around circumference
Count from base to tip
Default 56 lb/bu
Formula Used
Yield (bu/ac) = (ears/1000ac × kernel rows × kernels/row × TW/56) ÷ 90,000
Ear count × 1000 = plants/acre (1/1000 acre row method). The 90,000 kernels/bu constant is the long-standing default (Iowa State); Purdue and Ohio State suggest 80,000–85,000 for modern hybrids, so the range above sweeps 65,000–95,000. Valid from the milk (R3) stage on. Expect ±20 bu/ac.
Ear count × 1000 = plants/acre (1/1000 acre row method). The 90,000 kernels/bu constant is the long-standing default (Iowa State); Purdue and Ohio State suggest 80,000–85,000 for modern hybrids, so the range above sweeps 65,000–95,000. Valid from the milk (R3) stage on. Expect ±20 bu/ac.
Field Sampling Best Practices
• Sample at least 3 locations per field, at least 200 feet apart and away from field edges.
• Avoid sampling spots you noticed from the road — select locations before walking the field.
• Count ear length in the designated 1/1000-acre row length for your row width (see table in Fast Facts → Crop Removal tab).
• Count kernel rows and kernels/row on 5 representative ears per location — not the biggest or smallest.
• Use actual weighed test weight from a grain probe sample if available — low test weight docks value.
• Average multiple locations — field variability of 30–50 bu/ac between zones is common.
• Avoid sampling spots you noticed from the road — select locations before walking the field.
• Count ear length in the designated 1/1000-acre row length for your row width (see table in Fast Facts → Crop Removal tab).
• Count kernel rows and kernels/row on 5 representative ears per location — not the biggest or smallest.
• Use actual weighed test weight from a grain probe sample if available — low test weight docks value.
• Average multiple locations — field variability of 30–50 bu/ac between zones is common.
Disclaimer: Pre-harvest yield estimates are informational only. Corn carries roughly ±20 bu/ac of uncertainty and soybeans ±25% or more, even with good sampling. Not a substitute for certified yield monitoring, combine data, or professional agronomic advice. Verify marketing, insurance, and input decisions with your CCA, crop insurance agent, and grain merchandiser. Not financial, agronomic, or legal advice.
Method: Yield Component Method (Nafziger, University of Illinois) · Referenced by
University of Wisconsin-Extension, University of Minnesota Extension, and Iowa State University Extension ·
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