How Big Should My Compost Bin Be? (With Table & Examples)


Many gardeners like to use compost in their gardens, and for good reason.  Compost is a great way to provide nutrients to plants while also recycling yard waste and kitchen scraps.

You can have a compost pile out in the open, or you can use a bin to keep things neat.  If you opt for a compost bin, you may be wondering what size it should be.

So, how big should your compost bin be?  A compost bin should have twice the volume of the finished compost that you want.  For example, if you want 100 cubic feet of compost, then your bin should hold a volume of 200 cubic feet.  This allows extra space for material that will break down as it is composted.

Of course, the exact size of your compost bin will depend on the size of your garden and the depth of compost you want to apply.  Some gardeners also choose to use 2 or 3 bins so that they can have different compost piles in various stages, so there is always a “new” pile and always a “finished” pile.

Let’s take a closer look at how to figure out how big your compost bin should be.

How Big Should My Compost Bin Be?

The size of your compost bin will depend on two things:

  • the size of your garden (dimensions are length and width for a rectangular plot)
  • the depth of compost you want per square foot (how thick the layer of compost will be)
compost bins
The size of your compost bin depends on the size of your garden and the depth of compost you want.

If you multiply these two numbers together, you’ll have the volume of compost you will need for your garden.

If you then double that number, you’ll know how much space you need in your compost bin.  This doubling accounts for the breakdown of the compost, which will lose about half its volume as it decomposes.

How do we know that we need to double the volume?  Well, according to the University of Wisconsin-Madison, the volume of a compost pile can reduce by 55% to 73% depending on the method used.

Similarly, Washington State University suggests that a compost pile will reduce by about half its volume during the hot composting phase.

The table below will help you to calculate the approximate size of compost bin that you will need, based on the compost bin volume.  The compost bin volume that you will need is calculated as follows:

(compost bin volume) = 2*(area of garden)*(depth of compost)

or

(compost bin volume) = 2*(length of garden)*(width of garden)*(depth of compost)

When taking your measurements, be sure to use consistent units!  Don’t mix up inches and centimeters or use inches for one dimension and feet for another.

Compost Bin Volume (cubic feet)Compost Bin Dimensions (feet)Compost Bin Volume (cubic meters)Compost Bin Dimensions (meters)
Up to 505x5x2Up to 1.41.5×1.5×0.6
50 to 10010x10x2
6x6x3
10x5x4
1.4 to 2.83x3x0.6
1.8×1.8×0.9
3×1.5×1.2
100 to 15015x5x2
10x5x3
6x6x4
2.8 to 4.34.6×1.5×0.6
3×1.5×0.9
1.8×1.8×1.2
150 to 20010x10x2
8x8x3
10x5x4
7x7x4
4.3 to 5.73x3x0.6
2.4×2.4×0.9
3×1.5×1.2
2.1×2.1×1.2
200 to 30015x10x2
10x10x3
9x9x4
5.7 to 8.54.6x3x0.6
3x3x0.9
2.7×2.7×1.2
300 to 40020x10x2
12x11x3
10x10x4
8.5 to 11.36x3x0.6
3.7×3.4×0.9
3x3x1.2
400 to 50025x10x2
21x12x2
17x10x3
12x11x4
11.3 to 14.17.6x3x0.6
6.4×3.7×0.6
5.2x3x0.9
3.7×3.4×1.2

Let’s take an example to see how this would work in practice.

Let’s say that you have a garden that is 30 feet long by 20 feet wide.  We’ll also assume that you want a layer of compost that is 2 inches (1/6 feet) deep throughout the entire garden.

Then according to the equation from above, the volume of the compost bin would have to be:

(compost bin volume) = 2*(length of garden)*(width of garden)*(depth of compost)

= 2*30*20*(1/6)

= 200 cubic feet

Based on the table above, we could use a compost bin with dimensions of 10 feet long by 10 feet wide by 2 feet tall.  This would make it easy to dig compost out of the bin, due to the short height.

We could also opt for a bin with dimensions of 7 feet long by 7 feet wide by 4 feet tall.  This would be a good option if you need to save space (this bin would have half the area of the previous one).

In fact, we could even opt for a cube-shaped bin that is 6 feet on each side and 6 feet tall (6*6*6 = 216 cubic feet).

If you are handy, you could build any of these compost bins out of wood.  If you are not, or if you are pressed for time, you could buy an existing bin with the right dimensions.

If you cannot build or find a compost bin with the proper dimensions, don’t worry.  You can calculate the dimensions of any bin if you multiply the length, width, and height together.  This will tell you if it will hold enough compost for your garden.

For example, a bin that is 8 feet long by 8 feet wide and 4 feet deep would have a volume of 8*8*4 = 256 cubic feet, which would be large enough (with extra space) for the garden in our example.

However, a bin that is 6 feet long by 6 feet wide and 3 feet deep would have a volume of 6*6*3 = 108 cubic feet, which would not be large enough for the garden in our example.  (Two such bins would work though!)

Can You Use a Normal Bin for Compost?

Yes, you can use any ordinary container (trash barrel, bin, or container) for compost.  However, you might need to make some modifications so that it is better suited to its new purpose as a compost bin.

Before putting any yard waste in your compost bin, drill some holes into the sides.  This allows for fresh air (with oxygen) to move into the compost, and it also allows excess water to drain out.

You might also want to build a hatch into the side of the bin to make it easier to shovel finished compost out of the bin.

pitchfork
If you want to reduce the amount of shoveling you do, then put a hatch on the side of your compost bin.

If you build your own compost bin out of wood, be sure to avoid pressure-treated wood.  Pressure-treated wood contains chemicals that you probably do not want in your garden soil.

You may also want to avoid using plastic containers that held chemicals that you do not want in your garden.

What is the Best Compost Bin Design?

The best compost bin design has two or three separate chambers.  This design takes into account the fact that composting happens in different stages.

compost bin
You may want to have two or three compost bins of the proper volume. That way, you can store finished and unfinished compost separately.

For example, you can have one bin to store “finished” compost that is completely decomposed, cool, and ready to add to the garden.  You can have another bin for “unfinished” compost, which has partially decomposed but is still hot.

A third bin could be used to move “unfinished” compost back and forth to turn it.  Turning your compost helps to aerate it, and also ensures that the materials are evenly mixed.  Both air and even mixing will help compost to break down faster.

Instead of using compost bins, you can opt to use a compost tumbler.  A compost tumbler is a container mounted on a stand, with handles that allow it to be turned without a pitchfork or shovel.

You can use two different tumblers side-by-side to keep “finished” and “unfinished” compost separate, as mentioned above.

Whether you have a bin or a tumbler, it helps to have an opening to remove compost when it is finished.  This is often achieved by a hatch on the side of a compost tumbler, or a hatch on the side (near the bottom) of a compost bin.

That way, you can open the hatch and let the compost fall (with minimal shoveling) right into your wheelbarrow for easy transport to the garden.

How Often Should You Turn Compost?

You should turn your compost pile one or two times per week.  Continue doing this for as long as the pile continues to steam when it is turned.

This steaming happens due to the heat generated by bacteria in the compost pile.  Believe it or not, temperatures in a compost pile can get up to 140 degrees Fahrenheit (60 degrees Celsius).

If the pile does not seem to be breaking down, despite turning it frequently, then it is probably too dry.  In that case, you may need to add some water by spraying the pile with a hose.

If the compost pile develops a foul odor, it may be too wet, in which case you should add some dry material (such as sawdust or fallen leaves) to soak up some of the excess moisture.  Foul odors may also occur early on if you add manure to your pile, but these odors should disappear over time.

garden hose
If your compost is too dry, add some water to help it decompose.

For more information, check out this article on composting from the University of Missouri Extension.

How Long Does it Take for Compost to be Ready to Use?

According to the Iowa State University Extension, compost can take anywhere from 2 months to 1 year before it is ready to use.

On average, a compost pile will probably take 6 to 8 months before it is completely decomposed and ready for use in your garden.  However, a well-managed compost pile will decompose more quickly.

This requires regular turning to mix the materials and provide aeration.  It also requires a good mixture of green (nitrogen-rich) and brown (carbon-rich) materials in the compost pile.

sawdust
Sawdust is a “brown” (carbon-rich) material that you can add to your compost pile. It can dry things out if the pile is too wet.

For more information on green and brown materials, check out my article on how to make compost.

In addition, you will need to maintain proper moisture levels in your compost pile.  This means adding water if the pile is too dry or adding dry material if the pile is too wet.

Finally, make sure not to put things in your compost pile that will not break down quickly, or things that will attract pests.

For more information, check out my article on things you should not put in your compost pile.

Conclusion

By now, you have a good idea of how big your compost bin should be, based on the size of your garden and the amount of compost you need.

I hope you found this article helpful – if so, please share it with someone who can use the information.  If you have any questions about compost bin sizes, please leave a comment below.

jonathon.david.madore

Hi, I'm Jonathon. I’m the gardening guy (not guru!) who is encouraging everyone to spend more time in the garden. I try to help solve common gardening problems so that you can get the best harvest every year!

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