Last updated: June 19, 2026
Corn Yield Calculator
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Quick Answer
The Corn Yield Calculator estimates pre-harvest corn yield using the yield-component method: Yield (bu/acre) = (Ears per acre × Kernels per ear) ÷ Kernel factor, where the kernel factor is about 80,000 (large kernels), 85,000 (average), or 90,000 (small/stressed). For example, a field with 32,000 ears/acre and 16 × 32 = 512 kernels per ear at an 85,000 factor yields about 192.8 bu/acre, or 12.1 t/ha. Sampled at the dent (R5) stage from at least 5 sites in the field, the method is typically accurate to ±10% of the harvested combine yield.
Corn yield in bushels per acre equals ears per acre times kernels per ear, divided by a kernel factor of about 85,000. For example, 32,000 ears per acre with 512 kernels per ear gives roughly 193 bushels per acre, or about 12 tonnes per hectare.
Key Takeaways
- Yield (bu/acre) = (Ears per acre × Kernels per ear) ÷ Kernel factor — three numbers, one divisor
- Kernel factor: 80k for large kernels (great year), 85k average, 90k for stressed/small kernels
- 1/1000 acre = 17.4 ft of row at 30-inch spacing — count ears in this strip and multiply by 1000
- Sample at the dent (R5) stage from at least 5 sites for ±10% accuracy versus the combine
- 1 bu/acre ≈ 0.0628 t/ha (corn at 56 lb/bu, 15.5% moisture)
- Drop tip-back kernels — they look like grain but never make it to the elevator
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Formula
Yield (bu/acre) = (Ears per acre × Kernels per ear) ÷ Kernel factor
Where:
- Y=Yield estimate(bu/acre)
- E=Ears per acre (population × ears/plant)
- K=Average kernels per ear
- F=Kernel factor (kernels per bushel, ~80,000–90,000)
Worked Examples
Good corn field — 32k ears, 16 × 32 kernels, 85k factor
A typical well-managed Corn-Belt field at standard population and average kernel size, sampled at the dent (R5) stage.
- 1Kernels per ear = 16 rows × 32 kernels/row = 512
- 2Yield = (32,000 × 512) ÷ 85,000 = 192.8 bu/acre
- 3≈ 192.8 × 0.0628 = 12.1 t/ha
- 4Revenue ≈ 192.8 × $4.50 = $867.6 / acre
Average field — 30k ears, 450 kernels, 85k factor
A field with slightly thinner stand and average kernel count — close to the US national average yield.
- 1Yield = (30,000 × 450) ÷ 85,000 = 158.8 bu/acre
- 2≈ 158.8 × 0.0628 = 9.97 t/ha
Drought-stressed field — small kernels (90k factor)
A field with smaller, lighter kernels from heat or drought stress: switch to the 90,000 factor to avoid over-estimating.
- 1Yield = (28,000 × 420) ÷ 90,000 = 130.7 bu/acre
- 2Compare with 85k factor: (28,000 × 420) ÷ 85,000 = 138.4 bu/acre — using 90k drops the estimate by ~6%
Introduction
The Corn Yield Calculator estimates corn (maize) yield in bushels per acre before harvest using the yield-component method developed by university extension agronomists. Sample three numbers in the field — kernels per ear, ears per acre, and an appropriate kernel factor — and the calculator returns yield in bu/acre and tonnes/hectare, plus a quick revenue estimate at $4.50/bushel. Sampled correctly at the dent (R5) stage, the method is typically accurate to within ±10% of harvested yield. Pair this tool with our acres per hour calculator, compost calculator, and fertilizer calculator for a complete field workflow.
How the Yield-Component Formula Works
The math comes from a simple unit conversion: total kernels in an acre divided by kernels in a bushel gives bushels per acre. The trick is the kernel factor — kernels per bushel — which varies with kernel size and grain density.
Yield (bu/acre) = (Ears per acre × Kernels per ear) ÷ Kernel factor
Kernels per ear = number of rows around the ear × kernels per row
Ears per acre = plant population × ears per plant (most modern hybrids set 1 ear/plant)
Kernel factor: ~80,000 (large kernels), 85,000 (average), 90,000 (small/stressed)
1 bushel of corn = 56 lb at 15.5% moisture
1 bu/acre ≈ 0.0628 t/ha (the calculator does the SI conversion for you)
How to Use This Calculator (Step by Step)
You'll get the most reliable estimate by sampling several spots in the field and averaging.
Wait until the dent stage (R5) — usually 3–4 weeks before harvest — when kernel set is final
Pick at least 5 random sites across the field, avoiding obvious thin or weed patches
At each site, measure 1/1000 acre (17.4 ft of row at 30-in spacing) and count ears — multiply by 1000 for ears/acre
Pull 5 representative ears and count rows around each ear × kernels per row, then average
Choose the kernel factor: 80k for fat kernels (great year), 85k average, 90k for drought/heat-stressed kernels
Enter the three numbers above. The calculator returns bu/acre, t/ha, and a per-acre revenue at $4.50/bu
Drop the bottom-tip kernels that didn't fill ("tip-back") from your kernels-per-row count — they won't make grain.
Yield Estimates by Kernel Count
Quick reference at the standard kernel factor of 85,000 and a population of 32,000 ears/acre. Move one column left or right to scale by population.
| Kernels/Ear | Yield at 32k ears/ac (bu/ac) | Yield (t/ha) | Rating |
|---|---|---|---|
| 350 | 132 | 8.3 | Below average |
| 400 | 151 | 9.5 | Average |
| 450 | 169 | 10.6 | Good |
| 500 | 188 | 11.8 | Very good |
| 550 | 207 | 13.0 | Excellent |
| 600 | 226 | 14.2 | Outstanding |
| 650 | 245 | 15.4 | Record potential |
How to Sample Corn in the Field
Sampling technique drives accuracy more than the math does. Following Purdue Extension AY-217-W, use this routine.
| Step | Action | Why it matters |
|---|---|---|
| 1 | Pick at least 5 sites randomly | Averages out field variability |
| 2 | Measure 1/1000 acre (17.4 ft of row at 30-in spacing) | Standard sampling unit — multiply ear count × 1000 |
| 3 | Count ears in the strip; ignore tassels and dropped ears | Live, harvestable ears only |
| 4 | Pull 5 representative ears from the same strip | Capture the ear-to-ear variation |
| 5 | Count rows around the ear × kernels per row | Both vary independently — measure both |
| 6 | Drop tip-back kernels that did not fill | These won't reach the elevator |
| 7 | Pick a kernel factor: 80k / 85k / 90k | Matches kernel size to bushel weight |
Row spacing matters. At 20-inch rows, 1/1000 acre is 26.1 ft; at 36-inch rows it's 14.5 ft. Use the row width that matches your planter.
Choosing the Right Kernel Factor
The kernel factor — kernels per bushel — is the single biggest source of error if you guess. It compensates for kernel size and grain density, both of which vary year to year.
80,000 — large, well-filled kernels in a great growing year (good water, no late stress)
85,000 — average kernels in a normal year (this is the default if unsure)
90,000 — small kernels from drought, heat stress at grain-fill, or late N deficiency
Switching from 85k to 90k drops estimated yield by about 6%, and from 80k to 90k by about 11%
Verify in late-season fields: weigh a measured volume of grain and back-calculate the factor
Factors Affecting Final Yield
Even a perfect sample can drift from harvested yield because conditions keep changing between R5 and the combine. Plan for the following.
- Tip-back:
unfilled kernels at the ear tip can reduce kernel count by 5–15%
- Ear drop:
roughly 1–2% loss for every week harvest is delayed past full maturity
- Test weight:
standard is 56 lb/bu — drought years can drop to 52–54 lb, lowering grade
- Harvest losses:
combine settings typically lose 1–3% even when running well
- Moisture:
yield at 15.5% moisture; wetter grain shrinks once dried
- Population variability:
thin or skip rows can cut local yield well below the field average
Common Mistakes to Avoid
Most yield-estimate misses trace to a handful of repeat errors:
Sampling too early (before R5/dent) — kernel abortion that hasn't happened yet inflates the estimate
Sampling only the best part of the field — averages get optimistic fast
Counting tip-back kernels that didn't fill — they look like grain but never make a bushel
Using one kernel factor blindly all year — kernel size really does change with weather
Forgetting row width when measuring 1/1000 acre — the 17.4 ft figure is for 30-inch rows only
Sampling only one or two ears — ear-to-ear variation is large; pull at least 5
Bushels, Tonnes & Hectares — Quick Conversions
If you trade in metric units or compare with international yields, these are the conversions used by the calculator.
| Quantity | Conversion | Example |
|---|---|---|
| Mass per bushel | 1 bu corn = 56 lb @ 15.5% moisture = 25.4 kg | — |
| Bushels/acre → tonnes/hectare | × 0.0628 | 180 bu/ac ≈ 11.3 t/ha |
| Tonnes/hectare → bushels/acre | × 15.93 | 10 t/ha ≈ 159 bu/ac |
| Hectare → acre | 1 ha = 2.471 acres | — |
| Tonne → bushel | 1 t corn ≈ 39.37 bu | — |
Corn-Yield Glossary
Quick definitions for the agronomic terms used throughout this calculator:
| Term | Definition |
|---|---|
| Bushel (bu) | A volume unit that for corn equals 56 lb of grain at 15.5% moisture. |
| Kernel factor | Kernels per bushel — typically 80,000 to 90,000 depending on kernel size. |
| Ears per acre | Plant population × ears per plant — the count of harvestable ears in one acre. |
| Yield component | One of the multiplicative factors that build up final yield (ears, kernels, kernel weight). |
| Dent stage / R5 | The reproductive stage when kernels show a hard dent — when this method is most accurate. |
| Tip-back | Unfilled kernels at the tip of the ear; should be excluded from kernels-per-row counts. |
| 1/1000 acre | A standard sampling strip — 17.4 ft of row at 30-inch spacing — used to scale to per-acre values. |
| Test weight | Mass of grain per volume; the corn standard is 56 lb/bu. |
Quick Reference Card
Corn Yield — Quick Reference
Quick reference • Corn Yield Calculator
bu/acre = (Ears × Kernels) ÷ Factor • Factor 80k / 85k / 90k • t/ha = bu/acre × 0.0628Valid range: Sample at dent (R5); 5+ sites; 1/1000 acre = 17.4 ft @ 30-in rows
Common Values
⚠ Watch Out
- •Don't sample before the dent stage (R5) — kernel abortion is still possible and you'll over-estimate
- •Don't use one kernel factor blindly — match it to kernel size (80k / 85k / 90k)
- •Don't count tip-back kernels that didn't fill — they won't make grain
- •17.4 ft of row is 1/1000 acre at 30-inch spacing only — adjust for narrower or wider rows
Pro Tips
- →Sample at least 5 random sites and average — single-site estimates are unreliable
- →Ignore obvious thin or weed patches; your goal is the field-representative average
- →Switch to a 90,000 factor in drought or heat-stressed years to avoid over-estimating
- →Cross-check your sampled estimate against the combine yield monitor for next-year calibration
FAQs
What is the corn yield formula?
Yield in bushels per acre equals (Ears per acre × Kernels per ear) ÷ Kernel factor. The kernel factor is the number of kernels in a bushel — typically 85,000 for average kernels, 80,000 for large/well-filled kernels, or 90,000 for small or stressed kernels.
How do I count kernels per ear?
Count the rows around the ear (usually 14–20, almost always an even number) and the average kernels per row down the length of the ear, then multiply. So 16 rows × 32 kernels per row = 512 kernels. Skip any unfilled tip kernels — they don't make grain.
How do I count ears per acre?
Measure 1/1000 of an acre — 17.4 ft of row at 30-inch spacing — and count ears in that strip. Multiply by 1000 to get ears per acre. Repeat at five random sites and average. For different row widths, length × row width must equal 43.56 ft² (1/1000 acre).
What is a good corn yield per acre?
The US average is around 175 bu/acre. A good field produces 200+ bu/acre, an excellent one 250+ bu/acre. The world record is over 600 bu/acre under contest conditions, and pre-WWII yields were just 20–30 bu/acre, so genetics, fertility, and equipment have transformed the crop.
When should I estimate corn yield?
The most reliable time is at the dent stage (R5), about 3–4 weeks before harvest, when kernel set is final but kernels haven't started to dry down hard. Earlier estimates often over-predict because some kernels haven't yet aborted.
How accurate is this estimate compared with the combine?
When sampled at R5 from at least 5 sites with a sensible kernel factor, the yield-component method is typically within ±10% of harvested yield. Single-site or pre-R5 samples can be much further off.
Why does the kernel factor matter so much?
It's the divisor — small changes move the answer a lot. Switching from 85,000 to 90,000 lowers your estimate by about 6%; from 80,000 to 90,000 by about 11%. Match the factor to kernel size: 80k for large, 85k for average, 90k for small/stressed.
How do I convert bushels per acre to tonnes per hectare?
Multiply by 0.0628 (corn at 56 lb/bu, 15.5% moisture). For example, 180 bu/acre ≈ 11.3 t/ha. To go the other way, multiply tonnes/hectare by about 15.93. The calculator returns both units automatically.
How many kernels are on a typical corn ear?
A normal ear has 14–18 rows with 25–40 kernels per row, so most ears carry 400–650 kernels. High-yielding hybrids in great years can exceed 700 kernels per ear; stressed plants may drop below 350.