Silage Calculator

Enter the dimensions of a bunker, drive-over pile (with flat top) or silo bag plus moisture and density to get gross and feedable tons as-fed and dry matter, herd feed days and the daily face removal rate.

Use the Silage Calculator

Silage Pile Inputs

Rectangular cross-section (L × W × H) — vertical walls, flat floor.

Enter interior dimensions in feet.

Editable planning assumption. Replace 15% with your storage and feedout records.

Calculated bulk density: ~40.0 lb as-fed/ft³

Herd Feedout Supply (Optional)

Results

Fill in the inputs and click Calculate.

Feedout Density Test (Measure Your Real Density)

UW-Madison storage density method: mark the face, weigh every load removed over several days, average the moisture of sampled loads, then measure how far the face moved back. Density = weight removed ÷ (face area × regression).

Bunker: top width = floor width. Pile: measure both. Bag: use floor width = top width = 0.785 × diameter and height = diameter.

Volume removed—
As-fed density—
Dry matter density—

Silo Bag Capacity Chart (13 lb DM/ft³)

Silage length = bag length − 2 × diameter; volume = π × D²/4 × silage length (Holmes, UW-Madison). As-fed tons assume 65% moisture. For another density multiply by density ÷ 13 (15 lb DM/ft³ → × 1.15).

Bag Silage length lb DM Tons as-fed
8 ft × 100 ft 84 ft 54,900 78
8 ft × 150 ft 134 ft 87,600 125
8 ft × 200 ft 184 ft 120,200 172
8 ft × 250 ft 234 ft 152,900 218
8 ft × 300 ft 284 ft 185,600 265
9 ft × 100 ft 82 ft 67,800 97
9 ft × 150 ft 132 ft 109,200 156
9 ft × 200 ft 182 ft 150,500 215
9 ft × 250 ft 232 ft 191,900 274
9 ft × 300 ft 282 ft 233,200 333
10 ft × 100 ft 80 ft 81,700 117
10 ft × 150 ft 130 ft 132,700 190
10 ft × 200 ft 180 ft 183,800 263
10 ft × 250 ft 230 ft 234,800 335
10 ft × 300 ft 280 ft 285,900 408
12 ft × 100 ft 76 ft 111,700 160
12 ft × 150 ft 126 ft 185,300 265
12 ft × 200 ft 176 ft 258,800 370
12 ft × 250 ft 226 ft 332,300 475
12 ft × 300 ft 276 ft 405,800 580

UW-Madison Benchmarks Used in the Checks

  • Packing density: below 14 lb DM/ft³, plan heavier or longer packing next harvest. Above 44 lb as-fed/ft³ is good; about 60 lb as-fed/ft³ is reachable with excellent management.
  • Face removal: at least 6 in/day from bunker and pile faces (12 in/day or more as a design value) and at least 18 in/day from bags.
  • Moisture: 65–70% for corn silage and 60–65% for hay silage in bunkers; above 70% loses juice.
  • Losses: storage loss about 8–10% with excellent management up to 28% with poor management, plus 3–15% at feeding and refusal.

Worked pile example: base 200 × 80 ft, 12 ft high, flat top 150 × 20 ft. Middle section = 175 × 50 ft. V = 12/6 × (16,000 + 4 × 8,750 + 3,000) = 108,000 ft³. At 14 lb DM/ft³ that is 756 tons DM, or 2,160 tons as-fed at 65% moisture before shrink.

Assumptions, privacy, and sources

  • All calculations run locally in your browser; the values you enter are not sent to an external calculation service.
  • Bunkers use a rectangular prism (L × W × H). Drive-over piles use the prismoidal formula with planar sloped sides and ends; a blank top gives a ridge (½ × L × W × H). Bags use a cylinder with silage length = bag length − 2 × diameter. Settling, bulging walls and irregular faces change the real volume.
  • Density, moisture, shrink, and TDN are user-controlled assumptions. Measure inventory and use a forage analysis for purchasing, ration, insurance, or lending decisions.
  • Hay equivalence uses net feedable dry matter and assumes each 1,400 lb hay bale is 85% dry matter. It is not a nutritional substitution ratio.

UW-Madison sources (Brian J. Holmes): Silage Bag Capacity, Storage Density spreadsheet documentation, Bunker Silo Sizing documentation.

Planning references: SDSU Extension silage resources, Manitoba Agricultural Services storage calculator, and Pioneer silage capacity reference.

Summary

Estimate gross packed and net feedable silage inventory in a bunker, a drive-over pile with sloped sides and a flat top, or a silo bag. Volume uses the prismoidal formula for piles and the University of Wisconsin bag method (silage length = bag length − 2 × diameter). Results include as-fed tons, dry matter, TDN, hay equivalent, herd feed days and the daily face removal rate, checked against UW-Madison targets (at least 14 lb DM/ft³; at least 6 in/day removal for bunkers and piles, 18 in/day for bags). A feedout test estimates your real density from weighed loads.

How it works

  1. Select the storage: bunker/trench silo (vertical walls), drive-over pile (sloped sides, optional flat top) or silo bag.
  2. Enter dimensions in feet. Piles use V = H/6 × (bottom area + 4 × middle area + top area); leave the top blank for a sharp ridge. Bags use V = π × D²/4 × (bag length − 2 × D).
  3. Pick a crop or enter moisture, dry matter (DM) density in lb DM/ft³ and TDN. As-fed density = DM density ÷ DM fraction.
  4. Set storage and feedout shrink; the 15% default is a planning value to replace with farm records.
  5. Optionally enter herd size and daily intake to get feed days and inches of face removed per day.
  6. Use the feedout density test (weighed loads ÷ volume removed) to replace the preset density with a measured one.

Use cases

  • Estimate how many tons of silage are in a bunker, pile or bag before the feeding season.
  • Distinguish gross harvested inventory from net feedable inventory by accounting for shrink.
  • Check whether a planned herd ration removes enough silage from the face each day to limit heating and spoilage.
  • Measure actual packing density from weighed feed-wagon loads and compare it with the 14 lb DM/ft³ target.
  • Look up silo bag capacity by bag diameter and length.
  • Calculate days of feed for the herd on an as-fed or dry matter basis.
  • Convert silage inventory to equivalent 1,400 lb dry hay bales on a dry-matter basis.
  • Support lender, insurance or forage-purchase inventory with a transparent calculation.

Frequently Asked Questions

Last updated: 2026-10-09 · Reviewed by Nham Vu