Silage Calculator
Find how much silage your herd needs for a feeding period, and the silo or bunker volume required to store it safely.
Typical Silage Intake by Animal
Common daily fresh silage ration ranges for reference.
How This Calculator Works
From herd ration to a physical storage volume.
What Is Silage and Why It Matters
Silage is fermented, high-moisture forage — commonly maize, sorghum, or grass — preserved through anaerobic fermentation rather than drying, letting farmers store a large volume of nutritious feed harvested at peak quality for use throughout the year, particularly through dry seasons when fresh fodder is scarce. Unlike hay, which relies on removing moisture to prevent spoilage, silage relies on excluding oxygen so that naturally occurring bacteria can convert plant sugars into organic acids that lower pH and stabilize the material against further decay.
Planning a silage program well means answering two connected questions: how much silage does the herd actually need across the planned feeding period, and how much physical storage volume does that translate into. This calculator answers both from a handful of inputs.
The Silage Calculation Formulas
Total Silage (kg) = Number of Animals × Daily Ration (kg) × Feeding Days
Total with Buffer = Total Silage × (1 + Buffer% ÷ 100)
Silo Volume (m³) = Total with Buffer (kg) ÷ Compacted Density (kg/m³)
If you provide your available silo length and width, the calculator also works out the storage height needed to fit the required volume, which is useful for checking whether a planned bunker or trench silo footprint is large enough.
How to Use This Calculator
- Enter your number of animals and their expected daily fresh silage ration.
- Enter your planned feeding period in days — often the length of the dry season or off-pasture period.
- Set a storage/spoilage buffer percentage to cover typical fermentation and face-spoilage losses.
- Adjust compacted silage density if you have a specific figure, or use the 700 kg/m³ default.
- Optionally enter your available silo length and width to see the required storage height.
- Tap "Calculate Silage Needs" to see total silage required, volume, and (if applicable) required height.
Why Storage Losses Matter
Even well-managed silage loses some dry matter to fermentation and surface spoilage — often in the range of 10 to 20 percent depending on how well the material was compacted, how tightly it was sealed, and how quickly the exposed face is used once the silo is opened. Building this loss into your production target from the start, rather than discovering a shortfall mid-season, is why this calculator includes an adjustable buffer percentage on top of the herd's raw consumption requirement.
Silo Types and Storage Considerations
- Bunker silo: An open, walled trench where silage is packed and compacted by driving equipment over it, then covered with plastic sheeting — common for medium to large operations due to relatively lower construction cost per tonne stored.
- Silage bags/tubes: Long plastic tubes packed using specialized equipment, offering flexibility in location and scale without permanent structure investment.
- Pit silo: A below-ground trench, often more affordable to construct but requiring good drainage to avoid water infiltration.
- Tower silo: A vertical structure less common in smallholder settings due to higher construction cost, but space-efficient on a small footprint.
Tips for Good Silage Quality
- Harvest at the right moisture content, typically 60-70% moisture for most silage crops — too wet risks seepage and poor fermentation, too dry makes adequate compaction difficult.
- Compact thoroughly and quickly. Good compaction excludes oxygen, which is essential for proper fermentation and long-term stability.
- Seal promptly and securely. Cover with quality plastic sheeting weighted down to exclude air, ideally within hours of filling being complete.
- Manage the face carefully once opened. Remove silage in a way that keeps the exposed face tight and minimizes the surface area exposed to air between feedings, which slows aerobic spoilage.
Final Thoughts
Silage planning connects two very different kinds of numbers — daily animal nutrition needs and physical storage engineering — into one practical figure you can act on well before harvest. Use this calculator during pre-season planning to confirm your silo capacity matches your herd's real needs, and revisit it whenever herd size, ration, or feeding duration changes.
Frequently Asked Questions
A typical lactating dairy cow consumes roughly 20 to 30 kilograms of fresh silage per day as part of a mixed ration, though this varies with body weight, milk yield, and how much other feed is included in the diet.
Divide your total silage weight requirement in kilograms by the typical compacted density of silage, usually around 650 to 750 kilograms per cubic metre, to get the storage volume needed in cubic metres.
Bunker size depends on total silage volume needed, which this calculator computes, and then on your available length and width — the resulting height should stay within a range your compaction equipment and loader can manage safely, typically not exceeding about 3 to 4 metres for smaller farm operations.
Proper compaction during silage-making removes air pockets and compresses the material considerably compared to loosely piled fresh forage, which is why compacted silage density is used for storage volume calculations rather than the loose, uncompacted crop's density.
Even well-managed silage typically loses some dry matter to fermentation and surface spoilage, often in the range of 10 to 20 percent depending on compaction quality, covering, and how quickly the face is used once opened, so many farmers add a buffer margin when calculating total silage to produce.
Maize (corn) is the most widely used silage crop globally due to its high yield and energy content, but sorghum, various grasses, and legume-grass mixes are also commonly ensiled depending on regional climate and availability.
Silage typically needs a minimum of about 3 weeks of sealed anaerobic fermentation before it's ready to feed, though many farmers wait 6 to 8 weeks or longer for a more complete, stable fermentation.
Both approaches work — a fixed daily amount is simpler when your herd is fairly uniform in size, while a body-weight-based percentage gives a more tailored estimate when animals vary significantly in size within the herd.