Engineering Notes Index

Minnesota/Wisconsin Engineering Notes
Spring 1999

Silage Bag Capacity

Brian Holmes, Wisconsin Extension Engineer

We frequently get questions about the amount of silage in a silo bag. One way to estimate this value is to calculate the volume in the bag and multiply by the silage density. The volume of a round bag is calculated as:

V = 3.14 x (D2 / 4) x L

where: V = Volume (ft3), D = Diameter (ft), L = Length of silage (ft)

When full-length bags are used, the length of silage is the bag length minus the unused portion needed to seal the end of the bag.

The quantity of dry matter in the bag is the volume multiplied by the dry matter (DM) density. The dry matter density can vary from bag to bag and depends on machine type and adjustment as well as forage type. Typical densities range between 11 and 15 lbs DM/ft3. Table 1 has been developed to show silo bag capacity based on the following assumptions.

Round Bags
Silage Length = Bag Length - (2 x Diameter)
Density = 13 lbs DM/ft3

Table 1. Capacities of silage bags at 13 lbs DM/ft3 density.

Bag Diameter

8 ft
8 ft
9 ft
9 ft
Bag Length (ft)
Silage Length (ft)
Capacity (lbs DM)
Silage Length
Capacity (lbs DM)
100
54
54,900
82
67,800
150
134
88,600
132
109,200
200
184
120,200
182
150,500
250
234
152,900
232
191,900
300
284
185,600
282
233,200
Bag Diameter

10 ft
10 ft
12 ft
12 ft
100
80
81,700
76
111,700
150
130
132,700
126
185,300
200
180
183,800
176
258,800
250
230
234,800
226
332,300
300
280
285,900
276
405,800

Use the multiplier in Table 2 to adjust the values in Table 1 for a different silage density. For example, the quantity of silage in a 200' 9' bag packed to 15 lbs DM/ft3 is:

150,500 lbs DM x 1.15 = 173,100 lbs DM

 

Table 2. Multiplier to adjust table 1 capacities to a different silage density.

Density (lbs DM/ft3)
Multiplier
11
0.85
12
0.92
13
1.00
14
1.08
15
1.15

Table 1 lists dry matter in one bag. If you need to know the capacity in lbs of silage as-fed (AF), divide the table value by the dry matter content. For example, the weight of 65% moisture silage that has a dry matter density of 13 lbs DM/ft3 in a 200-ft long bag of 9-ft diameter is:

Silage dry matter content = 100-65 /100 = 0.35

Silage weight as fed, lbs = dry matter weight/dry matter content

= 150,500 lbs DM/0.35

= 430,000 lbs

Silage weight as fed, tons = 430,000 lbs/2,000 lbs/T = 215 T

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