Grain Overdrying Penalty Calculator

What Is the Grain Overdrying Penalty?

Every year, grain farmers inadvertently leave thousands of dollars on the table by drying corn, soybeans, or wheat further below market moisture than necessary. The loss is invisible — there is no deduction on the scale ticket — but it is very real. When grain is delivered below the standard market moisture (15.5% for corn, 13.0% for soybeans, 13.5% for wheat), the buyer still pays for it at the standard bushel weight. You have essentially given away extra dry matter for free, while also burning fuel to remove moisture that had monetary value.

According to Pioneer agronomists, a farmer drying 100,000 bushels of corn and missing the target by just one moisture point leaves over $6,500 on the table. At the same time, ISU Extension notes that every 1 point of extra propane drying costs roughly $0.018 × propane price per bushel — wasted on top of the shrink loss.

How to Use This Calculator

• Commodity: Select corn, soybeans, or wheat. The USDA standard target moisture fills in automatically but you can override it.
• Actual Dried Moisture: What did your grain test at after drying? If it is below the target, you have overdried.
• Bushels & Acres: Enter total wet bushels and acres harvested so the tool can compute a per-acre impact.
• Prices: Enter your current grain price, propane cost, and electricity rate. These directly drive the dollar results.
• Use Rates: The ISU default of 0.018 gal propane/bu/point is the industry average. Use your own records if available.

The Formulas Explained

Why the shrink formula works this way: Moisture content is expressed on a wet basis (water ÷ total weight). As water evaporates, the dry matter fraction increases and the total mass decreases. The formula above correctly accounts for this non-linear relationship — the same derivation used by Ohio State (AGF-503) and the University of Arkansas (FSA-1078).

USDA Standard Grain Moisture & Bushel Weights

Note: Some buyers set corn at 15.0% or other values — always confirm with your specific elevator contract. Override the target moisture in the calculator as needed.

Frequently Asked Questions

• What is the standard market moisture for corn and soybeans?

  The USDA standard market moisture (also called "base moisture") is 15.5% for corn (56 lb/bu) and 13.0% for soybeans (60 lb/bu), with wheat at 13.5% (60 lb/bu). These are published in USDA handbook AH-697 and widely cited by Ohio State Extension (AGF-503) and the University of Arkansas (FSA-1078).

  When grain is delivered above these moisture levels, most elevators apply a moisture discount. When delivered below, no credit is given — the buyer simply receives more dry matter per bushel than the standard, which means the seller is effectively giving it away for free.

• How do you calculate bushel loss from overdrying grain?

  The formula, verified by Iowa State University and the University of Nebraska-Lincoln, is:

  shrinkFraction = 1 − (1 − targetMC%) ÷ (1 − actualMC%)

  For example, soybeans dried to 9% instead of the 13% target lose a shrink fraction of 1 − (0.87 ÷ 0.91) = 4.4% of bushels. On a 10,000-bushel load at $10/bu, that is 440 bushels × $10 = $4,400 lost — invisible on the scale ticket but real money out of your pocket.

• How much propane is wasted by overdrying grain?

  Iowa State University Extension (A2-31, Shouse, Hanna and Petersen) estimates an average of 0.018 gallons of propane per bushel per moisture point removed for high-temperature dryers, with a range of 0.010–0.025 gal depending on dryer type, column depth, and outdoor temperature. Drying corn 2 extra points on 50,000 bushels burns roughly 1,800 gallons of propane — worth about $3,240 at $1.80/gal. Those gallons produced no sellable value.

• Should I deliver grain wet or risk drying too far?

  ISU agronomists advise that if you must err, delivering slightly wet is usually better economically. Wet grain incurs a per-point docking charge from the elevator, but you are still selling the water weight. Overdried grain means you burned fuel removing water the buyer will not pay for, and then the buyer counts bushels using the standard weight — keeping the extra dry matter at no additional cost to them.

  That said, delivering grain significantly too wet risks spoilage, elevator rejection, and heavy docking charges. The ideal is precision: hit target moisture as closely as possible.

• Does overdrying affect grain quality beyond the shrink loss?

  Yes. Corn dried significantly below target moisture develops stress cracks, increasing kernel breakage during handling and elevator conveying — which can lead to dockage for excess broken corn and foreign material (BCFM) and reduces feed or milling value. Overdried soybeans become brittle, increasing shattering losses during auger and elevator transfer. Both crops also become harder to aerate back up to market moisture once they are very dry. These quality and handling costs come on top of the dollar shrink penalty this calculator computes.

• What is the difference between "market shrink" and "physical shrink"?

  Physical (moisture) shrink is the actual weight loss as water evaporates from grain — pure physics. Market shrink is the bushel adjustment an elevator charges when you deliver wet grain above the base moisture level — it often includes a small handling-loss factor (typically 0.5–1%) on top of pure moisture shrink. This calculator computes the physical/moisture shrink only — the revenue lost when you deliver overdried grain below base moisture at the standard bushel weight.

• Why does the penalty grow non-linearly with extra moisture points dried?

  Because moisture content is expressed on a wet-weight basis, each additional point of moisture removed at low moisture levels represents a larger fraction of total bushel weight than at high moisture levels. Removing 1 point from 20% corn costs less fuel than removing 1 point from 14% corn, but the shrink fraction becomes proportionally larger. The formula 1 − (1 − target) ÷ (1 − actual) captures this correctly — the further below target you go, the steeper the loss curve.