Calculator

Silage Volume & Bunker Tonnage Calculator

Convert bunker silo dimensions, drive-over piles, or ag bag volume into tons of dry matter and days of feedout. Useful for harvest planning, ration consistency, and feed-purchase timing.

Pile dimensions and density

Typical: bunker 14–16 (Holmes target ≥15), drive-over pile 10–13, ag bag 15–17.
Corn silage typically 32–38% DM. Haylage 35–55%.

Herd size (optional)

Silage portion of DMI, not total ration. Typical 25–32 lbs DM/cow/day on dairies where corn silage is ~50% of TMR DM. Total lactating-cow DMI is 50–60 lbs/day across all feeds.

The bunker silo volume formula

For a rectangular bunker:

Volume (ft³) = length (ft) × width (ft) × average depth (ft)

To convert volume to tonnage:

  • DM tons = (volume × density) ÷ 2000
  • Wet tons = DM tons ÷ DM percent (e.g., DM tons ÷ 0.35 for 35% DM corn silage)

Density rules of thumb

Density depends on storage type, packing equipment, and the operator. Industry references for dry matter density:

  • Bunker silos: 14–16 lbs DM/ft³ when properly packed.
  • Drive-over piles: 10–13 lbs DM/ft³ — looser than bunkers because there are no walls to compress against.
  • Ag bags: 15–17 lbs DM/ft³ depending on bagger machine.

Why these numbers matter

If you don't know inventory tonnage within a few percent, you can't accurately plan ration transitions, feed purchases, or harvest acreage for next year. The calculator on this page is good for an order-of-magnitude estimate. SilagePlan measures every pile on your farm with drone or satellite imagery and gives you accuracy that supports operational decisions, not just rough planning.

Further reading