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Dairy & Livestock Calculators

Silage Pit Capacity Calculator

Calculate bunker or trench silo volume, the tonnes of green fodder it holds and how many days it will feed your herd.

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Same as the top for straight walls.

Well-compacted maize or sorghum silage: 550–700 kg/m³.

kg/m³
%

Often 15–25 kg for an adult cow or buffalo.

kg

Optional – to see how many acres of maize or sorghum fill the pit. Maize for silage often gives 140–200 quintals per acre.

Enter the length, top and bottom width and depth of your silage pit or bunker, and see how many tonnes of silage it holds and for how many days it will feed your animals – plus the fodder area needed to fill it.

About the Silage Pit Capacity Calculator

Silage is green fodder – usually maize, sorghum or bajra – chopped at the right stage, packed tightly and sealed so it ferments and keeps for months. It carries a herd through the lean months after the rains and in peak summer, when green fodder is scarce and costly.

Before you harvest, you need to know how big a pit to dig and how long the silage will last. This calculator works out:

  • the volume of a trench, bunker or pit with sloping or straight walls,
  • the tonnes of silage it holds at your packing density,
  • the feeding days it gives your animals after normal losses,
  • and, optionally, the acres of fodder crop needed to fill it.

The biggest factor you control is packing. Tractor-packed silage can reach 650–700 kg per cubic metre; loosely trodden silage may be under 450, holds less and spoils more.

How to use the Silage Pit Capacity Calculator

  1. 1 Measure the pit length, width at the top and at the bottom, and the height the silage will reach.
  2. 2 Keep the density at 600 kg/m³ for well-packed silage, lower if you pack by foot.
  3. 3 Enter the losses you expect – 10–20% is common for pits covered with plastic and soil.
  4. 4 Enter the number of animals and kg of silage each gets per day, then press Calculate.

The formula we use

Volume (m³) = Length × (Top width + Bottom width) ÷ 2 × Depth
Silage (t) = Volume × Density (kg/m³) ÷ 1,000
Usable (t) = Silage × (1 − Losses%)
Feeding days = Usable (kg) ÷ (Animals × kg per animal per day)

Worked example

A trench 10 m long, 3 m wide at the top, 2.5 m at the bottom and 2 m deep, packed to 600 kg/m³, with 15% losses, feeding 10 cows 20 kg each a day.

  1. Volume = 10 × (3 + 2.5) ÷ 2 × 2 = 55 m³.
  2. Silage = 55 × 600 = 33,000 kg = 33 tonnes.
  3. Usable = 33 × 0.85 = 28.05 tonnes.
  4. Feeding days = 28,050 ÷ 200 = 140 days.

At 160 quintals of green maize per acre, you need about 2.06 acres to fill this pit.

Things to keep in mind

  • Harvest at the right stage. Maize is best at the milk-to-dough stage, with 30–35% dry matter.
  • Fill fast and seal well. Fill within 2–3 days, pack in thin layers and cover with plastic weighed down with soil or tyres.
  • Open one end only and remove a layer of at least 15 cm every day to limit spoilage.
  • Introduce silage gradually and feed it after milking to avoid flavour taint in the milk.

Frequently asked questions

How much silage fits in a pit?

Multiply the volume in cubic metres by the packed density. A well-packed pit holds about 0.55–0.7 tonnes of silage per cubic metre.

How much silage should a cow get per day?

An adult cow or buffalo is commonly fed 15–25 kg of silage a day along with some dry fodder and concentrate.

How long does silage keep?

Properly sealed silage keeps for a year or more. Once opened, it should be fed within a few months, removing a fresh layer every day.

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