Soil & Compost

Compost Ratio Calculator

Enter your compost bin size and how full it is to see exactly how much green and brown material to add, using the ideal 1-part-green to 2-parts-brown ratio.

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How to use the compost ratio calculator

Enter the length, width, and height of your compost bin in feet, then drag the slider to show how full it is right now. Press Calculate Compost Mix and you will see your bin’s total volume, the space still left to fill, and exactly how much green and brown material to add to reach the ideal balance. The slider updates the result live once you have calculated once, so you can experiment with different fill levels.

The green-to-brown ratio explained

Healthy compost depends on the balance between two kinds of material. Greens are moist and nitrogen-rich; browns are dry and carbon-rich. Microbes need both: nitrogen to build their bodies and carbon for energy. Too many greens and the pile turns into a wet, smelly mess; too many browns and it sits there doing nothing. A practical target is about 1 part green to 2 parts brown by volume, which is the ratio this calculator uses:

  • Bin volume = length × width × height
  • Space remaining = bin volume × (1 − current fill %)
  • Green to add = space remaining × 1/3
  • Brown to add = space remaining × 2/3

For example, a 3 ft cube holds 27 cubic feet. If it is already half full, you have 13.5 cubic feet to fill, which works out to about 4.5 cubic feet of greens and 9 cubic feet of browns.

Good greens and browns to use

Greens include vegetable and fruit scraps, grass clippings, coffee grounds, and fresh plant trimmings. Browns include dried leaves, shredded cardboard and paper, straw, and untreated sawdust. Keep a stash of browns nearby — bagged autumn leaves are perfect — so you can always balance a fresh load of kitchen scraps. Chop or shred bulky material to speed up decomposition, and keep the pile about as damp as a wrung-out sponge.

Speeding up your compost

Three things make compost finish faster: a balanced mix, enough moisture, and plenty of air. Turning the pile about once a week mixes everything together and pushes oxygen into the middle, where the hottest, fastest decomposition happens. A well-managed pile can reach finished, crumbly compost in roughly 8 to 12 weeks, while a pile left untouched can take many months. If the center feels warm, things are working; if it cools down, give it a turn.

Troubleshooting common problems

  • Smelly or slimy: too wet or too many greens — add browns and turn for air.
  • Dry and not breaking down: add greens and water until evenly moist.
  • Pests: bury food scraps in the center and avoid meat, dairy, and oily foods.
  • Slow even when balanced: chop materials smaller and turn more often to raise the temperature.

Frequently Asked Questions

What is the ideal compost ratio of greens to browns?

A good rule of thumb is roughly 1 part green (nitrogen-rich) to 2 parts brown (carbon-rich) by volume. Browns provide energy and structure while greens provide the nitrogen that microbes need to break everything down. This calculator uses that 1:2 ratio to tell you how much of each to add to fill your bin.

What counts as green material?

Greens are fresh, moist, nitrogen-rich materials. Common examples are vegetable and fruit scraps, grass clippings, coffee grounds, tea leaves, and fresh garden trimmings. They tend to break down quickly and can turn slimy or smelly if you add too many without enough browns to balance them.

What counts as brown material?

Browns are dry, carbon-rich materials. Examples include dried leaves, shredded cardboard and paper, straw, sawdust from untreated wood, and small woody prunings. Browns add bulk and air pockets, soak up excess moisture, and keep the pile from compacting or smelling.

Why does my compost smell bad?

A foul or ammonia smell usually means too many greens and not enough air, leaving the pile wet and oxygen-starved. Mix in more browns such as dried leaves or shredded cardboard, turn the pile to add air, and it should recover within a few days. The 1:2 green-to-brown ratio helps prevent this in the first place.

How long does compost take to finish?

A well-balanced, actively managed pile that you turn about once a week and keep moist can produce finished compost in roughly 8 to 12 weeks. A cold or neglected pile that is left alone can take six months to a year. Turning adds oxygen and speeds up the microbes that do the work.

How often should I turn my compost?

Turning once a week is a good target for fast, hot composting. It mixes materials, redistributes moisture, and pushes fresh oxygen into the center where decomposition is most active. If the pile is hot and breaking down nicely, you can turn it a little less often; if it is slow or smelly, turn it more.

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GardenCalc Editorial Team

Horticulture writers & master gardeners

Our calculators and growing guides are written and fact-checked by gardeners with hands-on experience in vegetable production, soil management, and home landscaping.