Grain Moisture Adjustment Calculator

Why Adjust Grain Moisture?

Harvested grain rarely matches the moisture content preferred for storage or sale. For example, field corn might be harvested at 22–28% moisture, while many grain buyers pay based on a standard of about 15% moisture. If you simply compared wet weights, a high-moisture load could appear more productive than a drier load even if the amount of dry grain (starch, protein, and oil) is the same or less.

Adjusting to a common moisture basis removes the effect of water and allows an apples-to-apples comparison of yields, inventory, and marketing options. This matters for:

• On-farm records: Comparing varieties, fields, or management practices.
• Marketing decisions: Estimating how many saleable bushels you will have at the buyer’s standard moisture.
• Storage planning: Ensuring grain is dry enough to store safely without spoilage.

Drying grain removes water and reduces total weight, a phenomenon called shrink. Elevators and buyers usually do not pay for water that is removed before or during storage, so understanding shrink is directly tied to revenue and logistics.

Wet-Basis Moisture and Dry Matter

This calculator assumes moisture content is measured on a wet basis, which is standard in grain marketing. On a wet basis, moisture is defined as the mass of water divided by the total mass (water + dry matter), expressed as a percentage:

For example, if a sample weighs 100 kg and contains 15 kg of water, the moisture content is 15%, and the dry matter is 85 kg. When you dry grain, you are mainly removing water while trying to preserve dry matter. The goal of moisture adjustment is to keep the amount of dry matter constant while changing how much water is associated with it.

Moisture Adjustment Formula

To convert from one moisture level to another, the calculator uses a standard wet-basis adjustment formula. Let:

• W_w = wet grain weight at measured moisture
• M_w = measured moisture (%) on a wet basis
• M_d = desired (target) moisture (%) on a wet basis
• W_d = equivalent grain weight at the target moisture

The dry matter fraction of the wet grain is (100 − M_w) %, and the dry matter fraction at the target moisture is (100 − M_d) %. Because dry matter is assumed to be conserved, we set the dry matter before and after equal and solve for W_d:

Rearranging gives the working formula:

W_d = W_w × (100 − M_w) / (100 − M_d)

This is the formula implemented in the calculator. It simply scales the original wet weight so that the dry matter content remains the same after changing the moisture percentage.

Calculating Shrink

Shrink is the loss in total weight as moisture is removed. Using the wet and adjusted weights, shrink can be expressed as either a weight difference or a percentage:

• Weight shrink: W_shrink = W_w − W_d
• Shrink percentage: S (%) = 100 × (W_shrink / W_w)

In practice, this tells you how much of the original load’s weight was water that needed to be removed to reach the target moisture. Elevators may apply their own shrink and drying schedules, but the physical shrink calculated here is a useful baseline.

Worked Example

Suppose you deliver a truckload of corn with the following characteristics:

• Wet grain weight (W_w): 56,000 lb
• Measured moisture (M_w): 20.0%
• Target moisture (M_d): 15.0%

Step 1: Compute dry matter fraction at each moisture

• Dry matter fraction at measured moisture: 100 − 20.0 = 80.0%
• Dry matter fraction at target moisture: 100 − 15.0 = 85.0%

Step 2: Apply the adjustment formula

Use W_d = W_w × (100 − M_w) / (100 − M_d):

W_d = 56,000 × (80.0 / 85.0)

W_d ≈ 56,000 × 0.9412 ≈ 52,707 lb

So, after drying from 20% to 15% moisture, you would expect roughly 52,700 lb of saleable corn, assuming no additional handling losses or quality discounts.

Step 3: Calculate shrink

• Weight shrink: 56,000 − 52,707 ≈ 3,293 lb
• Shrink percentage: 100 × (3,293 / 56,000) ≈ 5.9%

This means about 5.9% of the original truck weight was water that needed to be removed in order to reach 15% moisture.

Typical Target Moisture Levels

Target moisture depends on crop, storage duration, and buyer policies. The table below shows common ranges used in many regions (always confirm local standards):

Use the buyer’s standard or your target storage moisture as the Target Moisture (%) in the calculator to see how much saleable grain you can expect from a wet load.

Interpreting the Calculator Results

After entering wet weight, measured moisture, and target moisture, the adjusted weight tells you how much grain you effectively have at the target moisture. Some practical uses include:

• Yield comparisons: Convert all loads to the same moisture before comparing fields, hybrids, or treatments.
• Marketing decisions: Estimate saleable bushels at elevator moisture standards to compare contract options.
• Drying decisions: Evaluate whether to dry grain on-farm versus delivering wet and letting the elevator dry it.

If the adjusted weight seems much lower than expected, check that moisture values are in percent on a wet basis, and confirm that your target moisture is realistic for the crop and market.

Units and How to Enter Data

The calculator is unit-agnostic for weight. You can enter:

• Pounds (lb)
• Kilograms (kg)
• Metric tons or short tons
• Any other consistent mass or weight unit

The output will be in the same unit you used for the wet grain weight.

If you track grain in bushels, convert bushels to weight first using an appropriate test weight (for example, 56 lb/bu for corn, 60 lb/bu for wheat, 60 lb/bu for soybeans, or the value measured on your farm). This calculator operates on weight, not volume, because moisture is a mass-based concept.

Moisture values should always be entered as percentages, not decimals. For example, enter 18.5 for 18.5% moisture, not 0.185.

FAQs

How do I choose a target moisture for my grain?

Use the moisture standard specified by your grain buyer or contract, or a moisture level considered safe for your intended storage duration in your climate. Extension publications and elevator policies are good references for typical targets by crop and region.

What is grain shrink?

Grain shrink is the reduction in total weight as grain is dried from a higher moisture to a lower moisture. Most of this shrink is simply water being removed. Elevators may add extra “management shrink” or charges to cover handling losses and operating costs.

Does this calculator include elevator shrink policies or drying fees?

No. The calculator only models physical shrink from water removal based on moisture percentages. It does not include any additional shrink factors, service fees, or price discounts that individual buyers may apply.

Can I use this for crops other than corn?

Yes. As long as moisture is measured on a wet basis and you use an appropriate target moisture for the crop, the same formula applies to soybeans, wheat, barley, canola, and many other grains and oilseeds.

Assumptions and Limitations

This calculator is designed to be transparent and straightforward, but like any simple model it relies on assumptions. Keep the following in mind when interpreting results:

• Wet-basis moisture only: The formulas assume moisture contents are reported on a wet basis. If you have dry-basis moisture values, convert them before using the tool.
• Dry matter is conserved: The calculation assumes that drying only removes water and that dry matter (starch, protein, oil, fiber) is not lost. In reality, a small amount of dry matter can be lost through handling, fines, and damage.
• No foreign material or quality discounts: The results do not account for foreign material, test weight changes, damage discounts, or grading factors that may reduce the paid weight or price.
• No elevator-specific policies: Physical shrink computed here may differ from shrink or drying charges applied by elevators, which can include additional factors for overhead and risk.
• Approximate guidance: Use this calculator for planning, comparison, and education. For settlement and contracts, always rely on official scale tickets and the terms specified by your grain buyer.

Background and References

The moisture adjustment formula and concepts used in this calculator follow standard wet-basis grain drying and shrink calculations commonly described in agricultural extension materials. Similar formulas are presented by many land-grant universities and grain marketing references. For detailed crop- and region-specific guidance, consult your local extension service or grain marketing adviser.