Compost Bin Size Calculator

A compost bin that is too small never gets hot, and one that is too big is hard to turn and slow to fill. This compost bin size calculator takes the length, width and height of a bin or pile and gives you its volume in cubic feet and cubic yards, the number of 30-gallon bags of leaves that fills it, and how much brown and green material to gather using the common mix of two parts browns to one part greens. It also shows roughly how much finished compost to expect. It works in feet, like the other tools on the site.

Fall is the best time to get started, because the leaves are free and the bags are sitting at the curb. Knowing the size of your bin tells you whether the leaves you can collect are enough to build a pile that will work, and how much kitchen waste and grass it will take to balance them.

How to use the compost bin size calculator

1. Enter the bin length in feet. Measure the inside of the bin, not the outside of the frame.
2. Enter the bin width in feet. Use the inside measurement.
3. Enter the height in feet. This is how high you will pile material. For a bin with a lid or top rail, use the working height inside.
4. Read the results. You get the volume in cubic feet, the volume in cubic yards, the leaf bags needed to fill it, the browns and greens to gather and the finished compost you can expect.

For round bins, work out the volume as 3.14 times the radius squared times the height, and use the cubic feet figure to plan. Tumblers and commercial bins list their capacity on the label, often in cubic feet or gallons, and you can use that number directly.

The compost bin math

The volume of a rectangular bin is length times width times height. Browns and greens are then split by volume, because composting recipes are given in volume ratios.

Volume (cu ft) = length (ft) × width (ft) × height (ft)
Cubic yards = cubic feet ÷ 27
Leaf bags = cubic feet ÷ 4.01, rounded up
Browns (cu ft) = volume × 2 ÷ 3
Greens (cu ft) = volume ÷ 3
Finished compost (cu ft) = volume ÷ 2, roughly

A 30-gallon bag holds about 4.01 cubic feet, which is why the calculator divides by 4.01.

Worked example: the classic 3 by 3 by 3 foot bin

A bin 3 feet long, 3 feet wide and 3 feet high holds 3 × 3 × 3 = 27 cubic feet, which is exactly 1 cubic yard. To fill it with leaves alone you would need 27 ÷ 4.01 = 6.7, so 7 bags of loose leaves. For a balanced pile, gather 18 cubic feet of browns and 9 cubic feet of greens. The finished compost will be roughly 13.5 cubic feet.

Worked example: a larger three-bay style bin

One bay of a larger system measures 4 feet by 4 feet by 3 feet, which is 48 cubic feet, or 1.78 cubic yards. It takes 48 ÷ 4.01 = 12 bags of loose leaves to fill. For a balanced mix, that is 32 cubic feet of browns and 16 cubic feet of greens, and you can expect around 24 cubic feet of finished compost.

Worked example: a small bin for a small yard

A compact bin of 2 feet by 2 feet by 3 feet holds 12 cubic feet, or 0.44 cubic yards. It fills with 3 bags of leaves, using 8 cubic feet of browns and 4 cubic feet of greens, for about 6 cubic feet of finished compost. A bin this small may not reach high temperatures, but it will still turn out compost, more slowly, and it suits the amount of waste from a small household.

Why the size of a compost pile matters

Composting is done by microbes that eat the material and give off heat as they work. A pile that is big enough holds that heat in, and the center warms up, which speeds the process and kills many weed seeds and some disease organisms. A pile of about 3 feet in each direction, or 1 cubic yard, is commonly recommended as the minimum size for a pile that heats up well. Much smaller piles lose heat to the air and compost slowly in a cooler, gentler way.

There is also a ceiling. Piles larger than about 5 feet in any direction are hard to turn, and the middle may get too little air. If you have more material than a 3 to 5 foot pile can hold, build a second bin next to the first, and use them in turn, with one filling while the other finishes.

Choosing a bin type

• Open pile: the cheapest option. It needs no materials, but it is untidy and can attract animals.
• Wire cage or wire and stake bin: inexpensive and breathable. A simple ring of hardware cloth about 3 feet across and 3 feet tall holds a cubic yard.
• Pallet bin: three or four wooden pallets wired together make a square bin, with good airflow and a front that you can open.
• Plastic bin with a lid: tidy and animal-resistant, and it holds moisture well, though airflow is limited, and many are smaller than the ideal.
• Tumbler: an enclosed drum that you turn with a handle, which makes mixing easy. Capacities are usually small, so check the label.

Whichever you choose, put the bin on bare soil where worms and microbes can reach it, in a spot that is convenient to the kitchen and to your garden, and out of the worst wind.

Browns and greens

Compost needs a balance of carbon-rich browns and nitrogen-rich greens. A common starting recipe is about two to three parts brown to one part green by volume. That is a mix of roughly two parts browns to one part greens in the calculator, and you can add more brown if the pile is wet or smelly.

Browns

• Dry leaves, which are the classic brown
• Shredded cardboard and paper
• Straw and dry plant stalks
• Sawdust and wood chips in small amounts

Greens

• Vegetable and fruit scraps
• Coffee grounds and tea bags
• Fresh grass clippings, as long as they have not been treated with herbicide
• Garden trimmings and spent plants

What to keep out

Leave out meat, fish, dairy and greasy food, which attract pests and smell. Do not add dog or cat waste, which can carry parasites, or plants that are diseased or covered in pests. Weeds that have gone to seed and invasive roots belong in the trash unless you have a hot pile. Avoid treated wood and coal ash. Our guide to coffee grounds in the garden explains how to use that popular green.

How to build a compost pile in fall

1. Choose and set up the bin. Pick a spot on bare soil, and set up a bin sized with the calculator.
2. Collect leaves. Gather them from your yard, and ask neighbors for their bags. The leaf mulch calculator helps you decide how many to keep for mulch and how many to compost.
3. Shred if you can. Mow over the leaves first. Shredded leaves break down faster and do not mat.
4. Layer or mix. Put down a layer of browns about 6 inches deep, then a layer of greens a few inches deep, and repeat. Mixing them together works too.
5. Wet each layer. The pile should be as damp as a wrung-out sponge. Add water as you build.
6. Cover it. A tarp or a lid keeps off the worst rain and snow, so the pile does not get soggy or wash out.
7. Keep adding. Put kitchen scraps in the middle, covered with leaves, and keep a bag of leaves nearby to balance them.

Moisture, turning and temperature

A compost pile needs air and moisture. The right dampness is that of a wrung-out sponge: when you squeeze a handful, it should release a drop or two. Turning the pile with a fork every week or two adds air and speeds things up. A hot pile can reach 130 to 160 degrees Fahrenheit in the center, which a compost thermometer will show. If it gets much hotter than that, turn it to cool it. Piles that are not turned still make compost, but it takes longer, and many gardeners are happy to wait six months to a year for a slow pile.

Troubleshooting

• Smells like ammonia: too many greens. Mix in more browns, such as leaves or shredded cardboard.
• Smells like rotten eggs: too wet or compacted. Turn the pile, and add dry browns.
• Not heating up: the pile may be too small, too dry or short of greens. Add water, greens and more material.
• Dry and not breaking down: add water and turn the pile.
• Attracts animals: avoid meat and dairy, bury kitchen scraps under leaves, and use a bin with a lid or wire mesh.

Composting in winter

Composting slows down as the weather cools, and small piles may freeze solid. That is fine. The microbes resume when it warms in spring, and you can keep adding material through winter. A larger pile holds heat better. A layer of straw or leaves over the top or bales around the sides insulates it, and a lid keeps out snow. Many gardeners fill a bin in fall, let it rest over winter and use the compost the next summer.

Using your finished compost

Compost is ready when it is dark, crumbly and smells like earth, and you can no longer recognize what went in, apart from a few woody bits. Because the pile shrinks as it breaks down, finished compost is often roughly half the volume you started with, or less. Use it to top-dress beds, mix into potting soil, feed vegetables and build new beds. The compost calculator shows how much you will need for your garden, and the no-till garden bed calculator shows how to build a bed with it. For raised beds, use the raised bed soil calculator, and for general filling the soil calculator. Compost also lowers how much fertilizer you need, and the garden fertilizer calculator shows how to work out the rest.

Fitting compost into your fall routine

A compost bin pairs well with the other jobs of the season. Leaves go to mulch and the compost pile, spent plants go to the pile, and empty beds can be sown with a cover crop, as covered in the cover crop seed calculator. The fall garden prep guide puts it all in order, the beginner’s guide to composting goes deeper on the process, and the garden planner helps you decide where the bin and the beds go.

Common compost bin mistakes

• Making the bin too small. Under about 3 feet each way, piles seldom heat up. Use the calculator and aim for a cubic yard.
• Making it too big. Piles over 5 feet are hard to turn and may lack air.
• Too many greens. Kitchen scraps alone turn slimy and smell. Balance them with browns.
• Leaving the pile dry. Dry material does not break down. Keep it as damp as a wrung-out sponge.
• Adding meat, dairy or pet waste. They attract pests and can carry disease.
• Putting the bin on concrete. Worms and microbes need soil contact. Choose bare ground.
• Forgetting to account for settling. Leaves compress as they break down, so expect to top it up.

Frequently asked questions