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Dairy & Livestock Calculators Quick visual guide

Silage Calculator

Calculate total silage required for your herd, bunker or trench pit volume and length, and days of supply with storage losses.

Enter your details

Cows, buffaloes, or heifers receiving silage.

Usually 8–15 kg when fed with straw & green fodder, or 20–25 kg as sole roughage.

kg/day

Commonly 120–180 days (summer or dry scarcity months).

days

Side-to-side width inside the trench or bunker.

Average depth of compacted silage (not pit wall height).

Well-compacted corn silage at 35% DM is 600–680 kg/m³.

kg/m³

Well-covered pits lose 8–12%; poorly sealed pits lose 15–25%.

%

Harvested at 1/2 to 2/3 milk line, typically 32–38% DM.

%

Hybrid silage maize typically yields 140–200 quintals (14–20 tonnes) per acre.

quintal/acre

Please note: This calculator provides a mathematical estimate based on the values entered. Recommended agricultural application rates can vary by crop, soil, product formulation, location and official agricultural guidance. Check the product label and local agricultural recommendations before application.

Making silage (fermented green fodder) is the most effective way to beat summer fodder scarcity and keep milk yield stable. Enter your herd size, daily silage allowance, feeding days and pit dimensions to calculate exact tonnes to store, pit volume, required length and crop area needed.

About the Silage Calculator

Illustration: Silage Calculator

Silage is preserved, fermented green fodder packed tightly under anaerobic (oxygen-free) conditions. When summer heat wilts pastures and green fodder becomes scarce or expensive, silage provides succulent, highly digestible green nutrition that maintains peak milk production.

Rule of thumb for small dairy farms

  • Density: Well-packed maize silage weighs about 640 kg per m³ (equivalent to the international standard of 14 lb DM per cubic foot).
  • Per cow allowance: 10 kg of silage per cow per day for 180 days equals 1.8 tonnes consumed, which requires about 2.0 tonnes packed into the pit after 10% storage loss.
  • Face management: To prevent secondary aerobic spoilage once the pit is opened, you must remove at least 15 to 20 cm across the entire face every day in warm weather. Sizing the pit with appropriate width prevents silage heating and spoiling.

How to use the Silage Calculator

  1. 1 Enter how many animals will be fed silage and how many kilograms per animal per day.
  2. 2 Enter the duration of the feeding period (e.g. 180 days for 6 dry months).
  3. 3 Enter your proposed pit width and silage depth.
  4. 4 Adjust density and expected storage losses if needed.
  5. 5 Press Calculate to see tonnes to store, pit volume, length, and acres of green fodder to plant.

Quick visual guide

Infographic: how the Silage Calculator works – what you enter, the formula and the result
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The formula we use

Daily Herd Need (kg) = Animals × Silage per Animal (kg)
Total Eaten (tonnes) = Daily Herd Need × Feeding Days ÷ 1,000
Silage to Store (tonnes) = Total Eaten ÷ (1 − Storage Loss %)
Pit Volume (m³) = Silage to Store (tonnes) × 1,000 ÷ Density (kg/m³)
Pit Length (m) = Pit Volume ÷ (Width × Height)
Crop Area (acres) = (Silage to Store × 10 quintals/t) ÷ Crop Yield (quintal/acre)

Worked example

You have 10 cows, feeding 10 kg silage per day for a 180-day summer season. The planned trench pit is 4 metres wide and 2 metres deep:

  1. Herd daily need = 10 × 10 = 100 kg/day.
  2. Consumed over 180 days = 100 × 180 = 18,000 kg (18.0 tonnes).
  3. After 10% storage loss: 18.0 ÷ 0.90 = 20.0 tonnes to pack.
  4. At 640 kg/m³ density: 20,000 ÷ 640 = 31.25 m³ pit volume.
  5. Length at 4 m wide × 2 m deep = 31.25 ÷ (4 × 2) = 3.9 metres (approx. 13 feet).
  6. At a corn yield of 160 quintals/acre, you need: (20 × 10) ÷ 160 = 1.25 acres of maize.

Things to keep in mind

  • Harvest timing (Milk line): Harvest maize when the kernels are at 1/2 to 2/3 milk line (dough stage) with plant moisture between 65% and 68%. Too wet causes effluent run-off and sour clostridial fermentation; too dry prevents tight packing.
  • Chop size: Chop fodder to 1.5–2.0 cm (1/2 to 3/4 inch). This allows maximum compaction with a tractor and maintains adequate rumen effective fiber.
  • Seal immediately: Cover with heavy UV-treated 200–250 micron polyethylene sheets and weigh down thoroughly with soil or used tires. Air ingress is the number one cause of silage rot.

Frequently asked questions

How much silage does one cow need for 6 months?

At 10 kg per day, one cow needs about 1.8 tonnes of silage over 180 days. Accounting for 10% storage loss, plan to store 2.0 tonnes of chopped green fodder per cow.

How big should a silage pit be for 10 cows?

For 10 cows fed 10 kg/day for 6 months (20 tonnes stored), a trench pit 4 metres wide, 2 metres deep, and 4 metres long (about 13 feet wide, 6.5 feet deep, and 13 feet long) provides roughly 32 m³ of capacity.

How many acres of maize are needed for 20 tonnes of silage?

A good hybrid fodder maize crop yields 150 to 180 quintals (15 to 18 tonnes) of green biomass per acre. You will need approximately 1.2 to 1.3 acres of maize to fill a 20-tonne pit.

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