Calculator
Silage Calculator: Pit Size & Days of Supply
Find out how much silage your animals need and how big the pit or bunker should be, or how many days your stored silage will last.
Calculate
Packing and loss settings
Example: 10 animals at 10 kg a day for 6 months.
Well-packed maize silage weighs about 640 kg per m³. Each cow eating 10 kg a day for 6 months needs about 1.8 tonnes fed, or 2 tonnes stored after 10% loss: roughly 3 m³ of pit.
How it works
- Silage needed = animals × kg per day × days ÷ (1 − loss).
- Pit volume (m³) = tonnes stored × 1,000 ÷ density (kg/m³). Pit length = volume ÷ (width × height).
- Days of supply = volume × density × (1 − loss) ÷ daily use. A round bag uses π × (diameter ÷ 2)² × length.
How much silage per cow per day?
The calculator starts at 10 kg per animal per day as an editable example. Actual intake depends on animal size, milk production, silage dry matter and the rest of the ration. Use your farm’s ration amount.
Tips for good silage storage
- Fill fast and pack hard in thin layers. Low density means more air, more spoilage and higher loss.
- Cover with plastic and weigh it down right after filling.
- Keep the feeding face clean and remove a full slice each day so the exposed silage stays fresh.
- Size the pit so you can feed back at least 15–20 cm a day across the face in hot weather.
New to silage? Read What is silage?
Questions farmers ask
How much silage does a cow eat per day?
It depends on body weight, milk yield and what else is in the ration. Where silage is fed alongside green fodder, straw and concentrate, 8–12 kg a day is a common starting amount on small farms. This calculator starts at 10 kg; change it to match your ration.
How much does a cubic metre of silage weigh?
Well-packed maize silage at 35% dry matter weighs about 640 kg per cubic metre as fed. That matches the commonly used packing target of 14 lb of dry matter per cubic foot (about 224 kg DM per m³).
How much silage is lost in storage?
In a study of bunkers and bags, dry matter losses averaged about 5–11% depending on position, with the loosest silage near the top and in bags losing most. Poorly packed silage can lose 17–20%. The calculator starts at 10%.
How big should my silage pit be?
Work out the tonnes you need for the feeding period, add storage loss, divide by density to get cubic metres, then choose a width and height you can pack and cover well. Use the first tab of this calculator for the sum.
Sources
- UNL CropWatch, Estimating the tonnage of silage in a bunker silo (14 lb DM/ft³, 35% DM)
- SARE, Dry matter loss in bunker and bag silage (metric poster)
Last reviewed 2026-10-10.