Grain Moisture Shrink Calculator

Why wet bushels and dry bushels are different quantities

A bushel of corn is 56 pounds of corn — including whatever water is in it. When you deliver 10,000 bushels at 20 percent moisture, you deliver 560,000 pounds, of which 112,000 pounds is water. Dry that same grain to 15 percent and the dry matter is untouched, but 32,941 pounds of water has gone up the drier stack. What is left weighs 527,059 pounds, which is 9,412 bushels. You did not lose 588 bushels of corn. You lost 588 bushels' worth of water.

That is water shrink, and it is arithmetic, not a fee. Every buyer in the world applies it, because they are buying grain at a stated moisture and you handed them grain at a different one. What varies between buyers is whether they compute it honestly from the dry-matter identity or apply a flat posted shrink factor that bundles in an allowance for handling loss and drier throughput.

Handling shrink is the second deduction and it is a real physical loss: fines that blow out of the drier, dust collected by the aspirator, kernels broken and screened off, grain left in the legs and pits. Typical schedules apply a fraction of a percent to a percent. It is not water, so it is deducted from the bushels that survive drying rather than from the wet bushels — which is why total shrink is always slightly less than the two percentages added together.

Knowing which is which matters when you compare offers. An elevator quoting 1.4 percent shrink per point on corn to a 15 percent base is charging 1.4 points against a physical water loss of 1.1765 points; the extra 0.2235 per point is their handling and service allowance, and it is worth exactly as much money as the drying charge printed beside it. Over 7 points that gap is 9.8 percent against 8.2353 percent, so on 10,000 bushels it is 156 bushels of difference in stated shrink, worth about $704 at $4.50 — small enough to overlook and large enough to read the ticket for.

The dry-matter identity, and why the denominator is 100 − Md

Grain moisture in the US grain trade is quoted on a wet basis: 20 percent moisture means water is 20 percent of the total weight, so dry matter is the other 80 percent. That convention is the one USDA's Federal Grain Inspection Service uses for official moisture determination under the United States Standards for Grain, and every commercial meter in the country is calibrated to it, so a settlement sheet and this calculator are speaking the same language. Drying removes water and nothing else. So the pounds of dry matter before and after must be equal:

wet weight × (100 − Mw) = dry weight × (100 − Md)

Rearranging gives the whole calculator. The dry weight, and therefore the dry bushel count, is the wet count times (100 − Mw) ÷ (100 − Md). For 20 percent down to 15 percent that ratio is 80/85 = 0.941176, so you keep 94.1176 percent of your bushels and shrink is 5.8824 percent.

The denominator is the part people get wrong. Shrink is not the moisture difference divided by 100 — that would give 5 percent, and it would be wrong by nearly a full percent of the load. It is the moisture difference divided by the dry-matter fraction at the target moisture. That is why shrink per point depends on where you are drying to, not on where you started: to a 15 percent base, each point is 100 ÷ 85 = 1.1765 percent; to a 13 percent base, each point is 100 ÷ 87 = 1.1494 percent. Wheat and soybeans sold at 13 percent therefore shrink slightly less per point than corn sold at 15 percent.

Handling shrink then multiplies rather than adds. If S_w is water shrink and S_h is handling shrink, the bushels you keep are (1 − S_w)(1 − S_h) of what you delivered. With 5.8824 percent water and 0.5 percent handling you keep 0.941176 × 0.995 = 0.936471, so total shrink is 6.3529 percent, not the 6.3824 percent you get by adding. The gap is small on one load and not small across a harvest.

Finally, the water itself. Pounds of water removed is wet weight times the same shrink fraction: 560,000 × 5/85 = 32,941 pounds on the example above. That figure is what sizes your propane bill, because a drier's fuel use scales with pounds of water evaporated rather than with bushels handled. The grain drying cost calculator takes it from there.

Reading the result: what the shrink number is telling you

The primary figure is the bushel count you will actually be paid for. Everything else on the page explains where the difference went, and each of those pieces points at a different decision.

Water shrink is not negotiable, but the target is. You cannot argue with 100 ÷ (100 − Md) per point, but you can decide where to stop drying. Every point you remove below the buyer's base moisture costs you fuel and gives away weight you are not paid for. Corn dried to 13 percent and sold on a 15 percent base gives up 2.30 percent of its bushels for nothing: 100 × 2 ÷ (100 − 13), since the two points come out of grain that would otherwise have been sold at the 15 percent base. Aim at the base moisture, allow a small margin for meter error and for the moisture the grain will lose in storage, and stop.

Handling shrink is where to push back. It is a contract term, not a law of physics. If a schedule applies a posted shrink factor that already exceeds the physical water shrink and a separate handling deduction, you are paying for the same loss twice. Ask which convention the factor uses.

The drying charge and the shrink move in opposite directions when you shop. A buyer with a low posted drying charge and a high shrink factor can net out worse than one with the reverse, and the crossover depends on how wet your grain is. Run both through this calculator at your actual harvest moisture rather than comparing the headline numbers.

Wet bushels are a delivery measurement, not an inventory. If you are checking bin contents against scale tickets, convert to dry bushels first — otherwise the tickets will always appear to exceed what the bin capacity calculator says the structure can hold, and you will chase a discrepancy that is only water.

One caution on meter accuracy: portable and inline moisture meters are calibrated by crop and can read differently from the elevator's official meter, and both drift with grain temperature. A half-point disagreement on 10,000 bushels at $4.50 is about $265. If you dry on farm and market at several outlets, check your meter against the buyer's at the start of harvest.

Shrink from any harvest moisture down to a 15 percent base

Generated from the same expressions the calculator runs. For a 13 percent base — wheat, soybeans, canola — replace the 85 in the denominator with 87, which makes each point worth 1.149 percent instead of 1.176 percent.

Mistakes that make a shrink calculation wrong

• Dividing the moisture difference by 100. Going 20 to 15 is not 5 percent shrink, it is 5.882 percent. The denominator is the dry-matter fraction at the target moisture, not the whole load.
• Adding water shrink and handling shrink. They compound. 5.882 plus 0.5 is 6.382; the true figure is 6.353, because handling is taken from the bushels left after drying.
• Applying a corn shrink factor to soybeans or wheat. Those crops sell on a 13 percent base, so the per-point shrink is 1.149 percent, not 1.176 percent.
• Comparing a drying charge without the shrink convention beside it. A cheap drying charge attached to a fat shrink factor can cost more than the reverse; only the net dollars per wet bushel delivered can be compared.
• Over-drying past the buyer's base. Every point below base is fuel spent and weight delivered without payment.
• Using wet bushels for inventory or yield. Convert to dry bushels before you check a bin, compare fields with the corn yield estimate calculator, or feed a number into a crop budget.

Key terms

Wet basis moisture

Water expressed as a percentage of total weight — the convention used throughout the US grain trade and by every commercial moisture meter. Dry-basis moisture, used in some engineering work, expresses water as a percentage of dry matter and gives a larger number for the same grain.

Water shrink

The bushel loss caused solely by removing water, fixed by the dry-matter identity at 100 ÷ (100 − target moisture) percent per point.

Handling shrink

An additional deduction covering fines, dust, breakage and invisible loss through drying and handling equipment. It is a contract term and typically runs from a few tenths of a percent to about one percent.

Shrink factor

The percentage deducted per point of moisture removed under a buyer's posted schedule. It equals the physical water shrink only when the buyer computes shrink from the identity rather than posting a rounded figure.

Base moisture

The moisture at which the buyer's cash bid applies without discount — 15 percent for corn and 13 percent for soybeans and wheat at most US markets.

Where shrink sits among the other harvest decisions

Shrink is one term in a longer sum, and reading it alone leads to the wrong call about when to harvest.

Field drying versus drier drying. Corn left standing loses moisture for free, but it also loses bushels to lodging, ear drop, wildlife and weather, and a late harvest risks the whole crop. The right comparison is the drying and shrink cost of harvesting now against the expected field loss of waiting, not shrink against zero.

Test weight moves with drying. Grain dried hard and fast can lose test weight, which affects grade and can trigger its own discount, while grain that comes off wet often gains test weight as it dries. Check the settlement grade as well as the moisture; the test weight calculator converts between the pound and volumetric definitions.

Storage moisture is not market moisture. Safe long-term storage for corn is drier than the 15 percent base the market pays at, because mould growth is governed by equilibrium relative humidity and grain temperature. Grain going into a bin for a year is normally taken lower than grain moving in a week, and the bushels given up are the price of that storability.

When a settlement sheet disagrees with your figures, work backwards from the ticket rather than arguing the percentage: take the gross wet pounds, the moisture and the settled bushels, and solve for the implied shrink factor. That single number tells you which convention the buyer used. Then set the price you need with the crop break-even price calculator and use this page to see what a given delivery nets against it.