Understanding Moisture Shrink When Drying Grain

Introduction

When you harvest grain at 25% moisture and sell it at 15%, you lose weight — and that lost weight is lost revenue. Understanding moisture shrink is critical for deciding when to harvest, whether to dry your own grain or pay the elevator, and how to price grain correctly. Yet many farmers underestimate shrink because they use simple subtraction instead of the correct formula.

This guide explains the science of moisture shrink, provides the exact formula for calculating weight loss, shows how to convert shrink into bushels and dollars, and covers the hidden costs of drying. We include a complete worked example for corn from field to delivery.

The Moisture Shrink Formula

The key insight is that moisture is measured as a percentage of wet weight, not dry weight. When you remove water, both the numerator (water) and the denominator (total weight) change. The correct formula for shrink percentage is: Shrink % = (Initial moisture % − Final moisture %) ÷ (100 − Final moisture %) × 100.

For example, drying corn from 25% to 15%: Shrink % = (25 − 15) ÷ (100 − 15) × 100 = 10 ÷ 85 × 100 = 11.76%. This means you lose 11.76% of the wet weight. The common mistake is to simply subtract: 25 − 15 = 10% shrink. That understates the loss by nearly 2 percentage points.

The equivalent formula for final weight: Final weight = Initial weight × (100 − Initial moisture %) ÷ (100 − Final moisture %). For 1,000 bushels of 25% corn dried to 15%: Final = 1,000 × 75 ÷ 85 = 882.4 bushels. You lost 117.6 bushels to water removal.

Shrink Factors by Crop and Moisture

Different crops have different standard moisture levels for sale and storage. Corn: 15.5% (USDA standard), wheat: 13.5%, soybeans: 13%, grain sorghum: 14%, barley: 14.5%, oats: 14%. Drying to these standards from typical harvest moistures results in predictable shrink.

Corn shrink reference: 20%→15.5% = 5.33% shrink; 25%→15.5% = 11.24%; 30%→15.5% = 17.16%. Wheat: 18%→13.5% = 5.20%; 20%→13.5% = 7.51%. Soybeans: 16%→13% = 3.45%; 18%→13% = 5.75%.

These are moisture shrink only. Handling shrink (broken kernels, dust, losses during transfer) adds another 0.2–0.5% on farms with good equipment, and up to 1% with poor handling. Total shrink = moisture shrink + handling shrink.

The Cost of Drying: Energy and Shrink

Drying grain costs money in two ways: the energy to remove water (propane, natural gas, electricity) and the lost weight from shrink. The energy cost depends on the drying method. High-temperature continuous-flow dryers use 0.02–0.03 gallons of propane per bushel per point of moisture removed. Low-temperature in-bin drying uses 0.01–0.015 gallons/bu/point but takes longer.

For example, drying 1,000 bushels of corn from 25% to 15% (10 points) with a high-temp dryer: propane = 1,000 × 10 × 0.025 = 250 gallons. At $1.50/gallon, that is $375 in fuel. Plus electricity for fans: approximately $0.02–$0.05/bu, or $20–$50 for 1,000 bushels.

The shrink cost is the revenue lost on the 117.6 bushels that evaporated. At $4.50/bu, that is $529.20. Total drying cost = $375 + $35 + $529 = $939, or $0.94 per original bushel. This is why harvesting at the right moisture matters so much.

Worked Example: 5,000 Bushels of Corn from 28% to 15.5%

You harvest 5,000 bushels of corn at 28% moisture. The elevator buys at 15.5% and charges $0.05/bu/point for drying, plus a 1% handling shrink. Corn price is $4.30/bu. Should you dry on-farm or deliver wet?

Step 1 — Moisture shrink: (28 − 15.5) ÷ (100 − 15.5) × 100 = 12.5 ÷ 84.5 × 100 = 14.79%.

Step 2 — Handling shrink: 1.0%. Total shrink: 15.79%.

Step 3 — Final bushels: 5,000 × (100 − 28) ÷ (100 − 15.5) = 5,000 × 72 ÷ 84.5 = 4,260 bushels. Lost: 740 bushels.

Step 4 — Elevator drying charge: 5,000 × (28 − 15.5) × $0.05 = $3,125.

Step 5 — Revenue: 4,260 × $4.30 = $18,318. Minus drying charge: $15,193 net.

Step 6 — On-farm drying cost estimate: propane = 5,000 × 12.5 × 0.025 = 1,563 gal × $1.50 = $2,345; electricity = $150; total = $2,495. Revenue after on-farm drying: 4,260 × $4.30 − $2,495 = $18,318 − $2,495 = $15,823. On-farm drying saves $630 in this scenario.

Common Mistakes and Pro Tips

Using simple subtraction (25 − 15 = 10%) instead of the correct formula. This understates shrink by 15–20% and leads to poor marketing decisions. Always use the division formula.

Forgetting handling shrink. Even with perfect moisture shrink accounting, you lose 0.3–1.0% to broken corn, dust, and transfer losses. Factor this into your inventory and budget.

Drying too aggressively. High-temperature drying above 180°F can cause stress cracks in kernels, reducing test weight and increasing breakage susceptibility. Keep corn drying air below 160°F for seed corn and 180°F for commercial corn.

Not aerating after drying. Grain coming out of a dryer is warmer than ambient. If you bin it without cooling, it will sweat and spoil. Run aeration fans for 12–24 hours after drying to bring grain to ambient temperature.

Ignoring the opportunity cost. Drying your own grain ties up equipment, labor, and management time. If your time is worth $50/hour and you spend 20 hours managing drying, that is $1,000 of hidden cost.

Conclusion

Moisture shrink is not simple subtraction — it is (initial − final) ÷ (100 − final) × 100. This formula gives the true weight loss when drying grain. Add handling shrink of 0.3–1.0%, factor in energy costs, and you have the complete picture of drying economics. Harvest as close to standard moisture as conditions allow, and compare on-farm drying costs against elevator charges before deciding.

For quick shrink calculations, use our Moisture Shrink Calculator. The Grain Bin Capacity Calculator helps plan storage, and the Grain Storage Calculator estimates total storage costs including drying.

Frequently Asked Questions

How do you calculate moisture shrink?

Shrink % = (initial moisture % − final moisture %) ÷ (100 − final moisture %) × 100. For corn from 25% to 15%: (25−15)÷(100−15)×100 = 11.76% shrink.

How much does corn shrink when drying?

From 25% to 15.5% moisture, corn shrinks about 11.2% in weight. From 20% to 15.5%, about 5.3%. Each point of moisture removed costs roughly 1.1–1.2% of the remaining weight.

What is the difference between moisture shrink and handling shrink?

Moisture shrink is weight lost to water evaporation. Handling shrink is weight lost to broken kernels, dust, and transfer losses — typically 0.2–1.0%. Total shrink is the sum of both.

Is it cheaper to dry grain on-farm or at the elevator?

It depends on propane prices, equipment efficiency, and elevator drying charges. Generally, on-farm drying is cheaper if you have efficient equipment and can manage it well, but elevator drying saves time and labor. Always calculate both options.