Silage Pile Volume Calculator

Overview: Estimating Silage Pile Volume and Feed On Hand

Silage stored in bunkers, trenches, or drive-over piles represents a major investment in feed. Knowing how much silage you actually have on hand is critical for:

• Planning feed inventories for the feeding season
• Checking whether you will need to purchase additional forage or byproducts
• Budgeting and cash flow management
• Ration formulation and monitoring shrink losses over time

This calculator estimates the volume of a silage pile or bunker based on simple field measurements. It then uses silage density and moisture content to estimate total as-fed tons and dry matter (DM) tons. The method is approximate but widely used in dairy, beef, and feedlot operations to support day-to-day decision-making.

How the Silage Pile Volume Calculation Works

Because silage piles do not have perfectly regular shapes, we use a geometric approximation. The cross-section of the pile (looking at it from the end) is modeled as a trapezoid. The pile is then treated as a long prism, where:

• Base width = width of the pile at ground level
• Top width = width across the crest or top of the pile
• Average height = average distance from the ground to the top of the pile
• Length = distance along the centerline of the pile

The process is:

1. Estimate cross-sectional area using a trapezoid.
2. Multiply by pile length to get volume in cubic feet.
3. Multiply by density (lb/ft³) to get total pounds of silage (as-fed).
4. Use moisture content to split pounds into water and dry matter, then convert to tons.

Trapezoid Area Formula

The cross-section is approximated as a trapezoid with parallel sides equal to the base width and the top width, and height equal to the average pile height. The area of a trapezoid is the average of the two parallel sides multiplied by the height:

Where:

• A = cross-sectional area (ft²)
• B = base width (ft)
• T = top width (ft)
• H = average height (ft)

In plain language, this is:

Area = ((Base width + Top width) / 2) × Average height

Volume in Cubic Feet

Once the cross-sectional area is known, pile volume is:

Volume (ft³) = Area (ft²) × Length (ft)

Assuming the pile’s cross-section is reasonably similar along its length, this gives a fair approximation of total cubic feet of silage in the pile.

From Volume to As-Fed and Dry Matter Tons

Volume alone does not tell you how much feed you have, because compaction, crop type, and moisture all affect density. The calculator uses the density and moisture inputs to estimate pounds and tons of feed on an as-fed and dry matter basis.

Step 1: Pounds of Silage (As-Fed)

First, the calculator multiplies volume (in cubic feet) by the density you enter (in pounds per cubic foot):

Total pounds (as-fed) = Volume (ft³) × Density (lb/ft³)

This gives the total weight of silage in the pile as it is fed, including water.

Step 2: Moisture and Dry Matter

Moisture content is entered as a percentage on an as-fed basis, for example 65% moisture for typical corn silage. The corresponding dry matter percentage is:

Dry matter % = 100 − Moisture %

The calculator then estimates the dry matter in pounds:

Dry matter (lb) = Total pounds (as-fed) × (Dry matter % / 100)

And converts to tons (1 ton = 2,000 lb):

Dry matter (tons) = Dry matter (lb) / 2,000

The as-fed tons are simply:

As-fed tons = Total pounds (as-fed) / 2,000

Typical Silage Densities and Moisture Ranges

Density has a large impact on total tons. Values vary with crop type, chop length, moisture, delivery rate, and packing tractor weight. The density field in the calculator is on an as-fed basis (lb/ft³). Typical ranges include:

• Corn silage (well-packed, 60–68% moisture): about 40–48 lb/ft³
• Haylage (grass or alfalfa, 55–65% moisture): about 32–40 lb/ft³
• High-moisture corn or sorghum (25–35% moisture): about 45–55 lb/ft³
• Poorly packed piles or very dry silage: may be 10–20% lower than typical values

If you have scale data from loads going into or out of a bunker, you can back-calculate a farm-specific density and enter that number for more accurate results.

How to Measure Pile Dimensions in the Field

Reliable estimates depend on good measurements. The following guidelines help keep measurements consistent and practical.

Length

• Measure along the centerline of the pile from one end to the other.
• Exclude very tapered or irregular end caps if they clearly contribute little volume, or measure them separately if desired.

Base Width

• Measure at ground level, perpendicular to the length of the pile.
• Use a tape, laser, or pacing; for very wide piles, two people can measure from each side and meet in the middle.
• Take a few measurements at different points and use an average if the base width is not uniform.

Top Width

• Measure across the top or crest where the pile is highest.
• If the pile is peaked, the top width may be close to zero; in that case, use a small value or leave it at zero as a reasonable approximation.
• For flat-topped piles or bunkers, measure from one shoulder to the other across the top surface.

Average Height

• Measure from ground level up to the top of the pile.
• Take several measurements at different points across and along the pile and average them.
• If you are using a bunker with walls, height is often measured from the floor to the highest silage level, not to the top of the wall.

Interpreting the Results

The calculator typically provides at least three key outputs:

• Volume (ft³): useful for comparisons and cross-checking densities.
• As-fed tons: the total tonnage of silage as it is fed, including water.
• Dry matter tons: the actual dry feed available for ration formulation.

Dry matter tons are especially important when comparing different feeds or planning rations, since animals eat based on dry matter intake (DMI), not water weight. A wetter silage will have more as-fed tons for the same dry matter, while a drier silage will have fewer as-fed tons but similar dry matter.

Using Results for Feed Planning

Once you know dry matter tons on hand, you can estimate how long the pile will last for a given group of animals:

1. Estimate average dry matter intake per head per day (lb DM/day).
2. Multiply by the number of head to get total DM required per day.
3. Convert that to tons per day (divide by 2,000).
4. Divide total DM tons in the pile by tons required per day to get days of feed.

This allows you to compare inventory against the planned feeding period and decide whether to adjust feeding levels, change rations, or line up additional forage sources.

Worked Example

Suppose you have a drive-over corn silage pile with the following measurements and assumptions:

• Length = 180 ft
• Base width = 70 ft
• Top width = 20 ft
• Average height = 12 ft
• Density = 40 lb/ft³ (as-fed)
• Moisture = 65%

1. Cross-Sectional Area

Area = ((Base width + Top width) / 2) × Height

Area = ((70 + 20) / 2) × 12 = (90 / 2) × 12 = 45 × 12 = 540 ft²

2. Volume

Volume = Area × Length = 540 ft² × 180 ft = 97,200 ft³

3. As-Fed Pounds and Tons

Total pounds (as-fed) = 97,200 ft³ × 40 lb/ft³ = 3,888,000 lb

As-fed tons = 3,888,000 lb ÷ 2,000 = 1,944 tons

4. Dry Matter Tons

Moisture = 65%, so dry matter = 35%.

Dry matter (lb) = 3,888,000 lb × 0.35 = 1,360,800 lb

Dry matter (tons) = 1,360,800 lb ÷ 2,000 = 680.4 tons DM

5. Days of Feed (Example)

If you plan to feed this pile to 400 cows, each eating 25 lb of DM from corn silage per day, then:

• DM per day = 400 × 25 = 10,000 lb DM/day
• DM tons per day = 10,000 ÷ 2,000 = 5 tons DM/day
• Days of feed = 680.4 ÷ 5 ≈ 136 days

This simple calculation shows whether the pile will cover your intended feeding period.

Comparison: As-Fed vs Dry Matter Basis

The table below summarizes the key differences between using as-fed tons and dry matter tons when evaluating silage inventories.

Assumptions and Limitations

The results from this calculator are estimates, not exact measurements. Keep the following assumptions and limitations in mind:

• Uniform cross-section: The method assumes the pile has a roughly constant cross-section along its length. In reality, piles often taper at the ends or bulge in the center, which can lead to some over- or underestimation.
• Trapezoid approximation: Shoulders and rounded tops are approximated by straight lines. For very rounded or uneven piles, the trapezoid model may slightly understate or overstate volume.
• Average measurements: Using single measurements for width and height assumes they are representative. For unusually irregular piles, taking multiple measurements and averaging them will improve the estimate.
• Density variability: The entered density is an average across the entire pile. In practice, density can vary by depth, location, and packing conditions. If you have weigh-back data or truck scale records, use those to refine your density input.
• Moisture basis: Moisture is assumed to be measured on an as-fed basis (e.g., 65% moisture). If lab results are on a dry matter basis, convert them appropriately before entering.
• Shrink and losses: The calculator estimates what is in the pile at the time of measurement, not what will actually be fed. Losses during feed-out (surface spoilage, wind, refusal) are not automatically accounted for and should be considered separately.

For high-stakes decisions or very large investments, consider confirming estimates with additional methods, such as periodic weigh-backs, loader bucket counts calibrated with scales, or consulting with a nutritionist or engineer familiar with your storage system.

Practical Tips and Related Uses

To get the most value from this calculator, consider the following tips:

• Re-measure piles periodically through the feeding season to track disappearance and shrink.
• Record densities that back-calculate well from actual feed-out data and use them as defaults for future years.
• Use dry matter tons, not as-fed tons, when comparing silage to alternative feeds or when evaluating changes in harvest moisture.
• If you manage multiple piles or bunkers, calculate each one separately and sum dry matter tons for a whole-farm inventory picture.

These practices improve confidence in your inventory numbers and help align feeding reality with ration formulations and budgeting assumptions.