Harvest Loss Calculator
Measure how much grain your combine leaves behind. Count kernels in 10 feet of row and instantly calculate yield loss per acre.
Harvest Loss Inputs
Count kernels left behind the combine
Count after combine pass
Typically 30"
Take multiple samples from different field locations and average them for the most accurate results. Avoid border rows and unusual spots.
All calculations use USDA-standard formulas. No registration required, works on mobile, tablet, and desktop.
What Is a Harvest Loss Calculator?
A harvest loss calculator measures how much grain your combine leaves in the field — a critical metric for evaluating combine performance and identifying adjustment issues. Even small losses add up: at $4.50/bu corn, losing just 2 bushels per acre across 1,000 acres means $9,000 in lost revenue.
Standard harvest loss is 1-2 bu/ac. Anything above 3 bu/ac indicates a problem with combine settings, operator technique, or field conditions. This calculator helps you quantify losses so you can take corrective action.
The method is simple: count kernels in a known area behind the combine, then convert to bushels per acre. The standard "20 kernels per 10 feet of row at 30-inch spacing" rule equals approximately 1 bushel per acre of loss.
Harvest Loss Formula
The standard formula for 30-inch rows:
Loss (bu/ac) = Kernels per 10 ft of row ÷ 20
For other row spacings, adjust proportionally:
Loss (bu/ac) = (Kernels ÷ 20) × (30 ÷ Row spacing in inches)
Example
You count 40 kernels in 10 feet of 30-inch row behind the combine:
40 ÷ 20 = 2.0 bushels per acre loss
At $4.50/bu and 1,000 acres, that's $9,000 — definitely worth adjusting the combine!
Types of Combine Loss
Pre-harvest Loss
Ears dropped before combine arrives. Check unharvested area for dropped ears.
Header Loss
Ears missed or dropped by corn head. Check header-width strip behind combine.
Cylinder/Rotor Loss
Kernels not threshed from cob. Check tailings and cobs for unthreshed kernels.
Sieve Loss
Kernels blown out the back. Check behind combine for loose kernels.
How to Reduce Harvest Loss
- Set corn head correctly: Snouts should gather all stalks. Stalk rolls should snap stalks cleanly without pulling ears.
- Match ground speed to conditions: 2.5-3.5 mph is typical for corn. Too fast increases header loss.
- Adjust cylinder/rotor clearance: Too tight = grain damage; too loose = unthreshed ears. Check every field.
- Set sieve and fan correctly: Start with manual recommendations, then fine-tune by checking loss behind combine.
- Harvest at proper moisture: 22-25% moisture is ideal. Drier corn shatters more; wetter corn doesn't thresh well.
- Inspect after every field: Take 5 minutes to check loss. Adjust settings as conditions change.
Frequently Asked Questions
Everything you need to know about corn yield calculation
Standard acceptable harvest loss is 1-2 bushels per acre, or about 1% of total yield. Losses above 3 bu/ac indicate a problem with combine settings or operator technique. Anything above 5 bu/ac should be investigated immediately.
Count kernels in a 10-foot section of row directly behind the combine pass. Every 20 kernels in 10 feet of 30-inch row equals approximately 1 bushel per acre of loss. Check pre-harvest loss first (before combine), then total loss behind combine.
Common causes include: wrong header height or speed, improper stalk roll adjustment, cylinder/rotor speed too high (grain damage) or too low (unthreshed ears), sieve/fan settings wrong, harvesting too dry (>18% moisture causes shatter), and operator fatigue.
At $4.50/bu corn and 1,000 acres, 1 bu/ac loss = $4,500 lost revenue. At $7/bu corn, that's $7,000. Reducing loss from 3 to 1 bu/ac saves $9,000-$14,000 per 1,000 acres — well worth the time investment in combine adjustment.
Try Our Other Free Farm Calculators
Browse 30+ free agriculture tools trusted by farmers across the USA, Canada, and Australia.
See All Calculators