Field-count conversion table
Approximate counts assume average seed size. Override the calculator factor when a local guide, seed count, or weighed sample is more representative.
| Crop | Count/ft² = 1 bu/ac | Count/10 ft² | Standard weight | Moisture basis | Uncertainty and source |
|---|---|---|---|---|---|
| Corn | 2 kernels | 20 | 56 lb/bu | 15.5% | Average kernels; ears must be weighed separately. Nebraska Extension, 2023. |
| Soybean | 4 beans | 40 | 60 lb/bu | 13% | About 3–5 beans/ft² by seed size; preset uses medium. Nebraska Extension, 2023. |
| Wheat | 20 kernels | 200 | 60 lb/bu | 13.5% | UGA approximation; southern guidance reports 17–20/ft². UGA Extension, reviewed 2012. |
| Barley | 14 kernels | 140 | 48 lb/bu | 14.5% | Typical varieties; southern guidance reports 14–15/ft². UGA Extension. |
| Oats | 10 kernels | 100 | 32 lb/bu | 14% | Southern guidance reports roughly 10–14/ft². UGA Extension. |
| Sorghum | 31 seeds | 310 | 56 lb/bu | 14% | Seed size varies; current Arkansas guidance reports 16–21/ft², so override locally. Arkansas Extension, 2025. |
| Canola | 115 seeds | 1,150 | 50 lb/bu | 8–10% harvest range | Very sensitive to seed size and discharge concentration. Oklahoma State Extension, 2017. |
| Rice | 22 grains | 220 | 45 lb/bu | Contract/local basis | Texas guidance gives about 21–24 grains/ft² by variety; preset uses the midpoint 22. Texas A&M AgriLife, 2007. |
Bushel weights and listed moisture conventions follow USDA NASS price-program guidance where available. A bushel weight is a marketing conversion, not a prediction of kernels per bushel.
Worked examples
Corn: kernels in 10 ft²
Behind-combine average = 24 kernels. 24 ÷ 10 = 2.4 kernels/ft²; 2.4 ÷ 2 = 1.2 bu/ac total loss. With 4 pre-harvest and 14 header-zone kernels: pre = 0.2, header = (14−4)÷10÷2 = 0.5, separator = (24−14)÷10÷2 = 0.5 bu/ac. At 200 bu/ac, loss = 0.6%; over 160 acres total = 192 bu; at $4.75/bu value = $912.
Soybean: baseline vs combine
In a 10-ft² frame, averages are 12 beans before harvest, 28 before discharge, and 52 behind the combine. At 40 beans/10 ft² per bu/ac: pre = 12÷40 = 0.3; header = (28−12)÷40 = 0.4; separator = (52−28)÷40 = 0.6; total = 1.3 bu/ac. At 55 bu/ac, that is 2.36%; 80 acres lose 104 bu worth $1,248 at $12/bu.
Vegetable or hand harvest: weighed sample
A cleaned 200-g sample from 10 ft² equals 20 g/ft². 20 × 107,639.1 ÷ 1,000 = 2,152.8 kg/ha. Against 12,000 kg/ha expected yield, loss is 17.94%. Across 1.62 ha, total loss is 3,487.5 kg; at $0.80/kg, gross value is about $2,790. The loaded custom example uses equal 1-ft header and collection widths, so no concentration correction is needed.
Target guide: interpret, then inspect
Acceptable loss is not universal. It depends on crop, yield, seed size, moisture, lodging, machine, throughput, and whether the figure means total field loss or machine-only loss. This calculator compares the field-count target with machine-only loss; the yield-comparison target applies to total loss.
Below target
Current measured loss is at least 0.25 percentage points below the entered target. Keep monitoring as crop and moisture conditions change.
Near target
Current loss is within 0.25 percentage points of target. Repeat samples before deciding whether adjustment is worthwhile.
Above target
Confirm the dominant zone, inspect the relevant components, and change one setting at a time while following the operator manual.
Named examples, not defaults: Oklahoma State soybean guidance (2021) uses no more than 3% total loss; Arkansas sorghum guidance (2025) describes 5% or less total loss as a realistic goal and 2–3% for threshing/separation in good conditions; the Canola Council explains why a manager may choose roughly 1–3% depending on timeliness and throughput.
Formulas and assumptions
Count loss (bu/ac) = average count ÷ frame ft² ÷ crop factor (count/ft² per bu/ac)
Weight loss (lb/ac) = cleaned sample lb ÷ frame ft² × 43,560 ÷ concentration factor; concentration factor = header width ÷ discharge width for rear drop-pan samples
Header loss = Zone B cumulative loss − Zone A pre-harvest loss; separator loss = Zone C total loss − Zone B cumulative loss; machine loss = Zone C − Zone A
Moisture-adjusted quantity = wet quantity × (100 − original moisture) ÷ (100 − comparison moisture)
Loss % = loss per area ÷ expected yield × 100; total loss = loss per area × field area; gross value = total loss × price
Field-count factors approximate grain at a conventional market basis and assume the averages represent the field. The weight method requires cleaned marketable grain. Results do not account for quality discounts, handling cost, sampling error, or whether grain can actually be recovered.
Methodology and page responsibility
This page translates cited extension sampling methods into transparent arithmetic. It has not been represented as reviewed by an agronomist or machinery specialist. Use local extension recommendations, contract specifications, and the machine operator manual for final decisions.
Conversion-factor change log
- 31 August 2026: added editable presets for corn, soybean, wheat, barley, oats, sorghum, canola, and rice; added source-level calculations, collected-weight scaling, and moisture normalization.
- 31 July 2026: initial yield-comparison calculator published.
Frequently asked questions
How many corn kernels per square foot equal one bushel per acre?
About two average corn kernels per square foot, or 20 in a 10-square-foot frame, equal 1 bu/acre according to Nebraska Extension and UGA guidance. Kernel size varies, and whole ears should be weighed or converted separately.
How many soybeans per square foot equal one bushel per acre?
About four medium soybeans per square foot equal 1 bu/acre. Nebraska Extension gives approximately three for large beans, four for medium beans, and five for small beans, all at a 60 lb/bu and 13% moisture basis.
How large should a harvest-loss sampling frame be?
A 10-square-foot frame is common for corn, small grains, and soybean ground counts. UGA Extension publishes across-swath dimensions; for example, a 12-foot cut needs a 10-inch travel distance to enclose 10 ft². Smaller drop pans can work for cleaned grain weight if their exact area and the combine concentration factor are used.
How many locations should I sample?
LSU AgCenter recommends at least three ground counts at each location; repeat across several representative field locations. This calculator defaults to five locations because more replication helps when yield, lodging, terrain, or moisture varies.
Where do I measure header loss versus separator loss?
UGA Extension places the pre-harvest baseline in standing crop, the gathering-loss check immediately ahead of the machine after it backs away, and total loss behind the machine. Subtraction isolates header and separator contributions.
Do whole ears, heads, or pods count?
Yes. They can contain substantial marketable grain. Shell or weigh their grain and add it to the correct zone; do not count one ear, head, or pod as one kernel. Nebraska Extension uses a separate corn-ear method based on ear weight and a fraction of an acre.
What is an acceptable combine loss?
There is no universal number. Crop, conditions, throughput, and whether the figure is total or machine-only loss all matter. Examples include no more than 3% total loss in Oklahoma State soybean guidance and 2–3% threshing/separation loss for grain sorghum in good conditions from Arkansas Extension.
How does grain moisture change the answer?
Water changes measured weight. Comparing yields at different moistures can look like physical loss even when dry matter is unchanged. The normalization formula follows the dry-matter approach explained by University of Florida IFAS Extension: adjusted quantity = wet quantity × (100 − original moisture) ÷ (100 − comparison moisture).
Can I use the calculator for vegetables or hand-harvested crops?
Yes. Use the collected-weight option with a custom crop, exact sampled area, and a one-pound reference unit, or use the yield-comparison tab with any consistent weight, box, or generic-unit basis.
Are my crop data stored?
No. The calculation runs in the browser, and this tool does not send or store the values entered.