Compost Bin Size Calculator
Size a compost bin from your weekly kitchen scraps and yard waste and how long material sits, with the volume in cubic feet and a suggested cube dimension.
How it works
Volume (gal) = (greens + browns per week) × retention weeks · Cubic feet = gallons ÷ 7.48 · Cube side = ∛(cubic feet)
A compost bin has to hold everything you add over the time it takes the oldest material to finish, so both your weekly volume and the retention period drive the size. There is also a lower bound: a pile needs to reach about one cubic yard (27 cubic feet) before its own mass insulates the core enough to heat up and compost quickly — smaller heaps still work but stay cool and break down slowly. Aim for a rough balance of browns (carbon: leaves, straw, cardboard) to greens (nitrogen: scraps, grass), keep the pile as moist as a wrung-out sponge, and turn it to add air; the material also shrinks substantially as it decomposes, so a bin sized this way rarely overflows.
Worked example
Adding 5 gallons of kitchen scraps and 10 gallons of yard waste a week (15 gal) with a 6-week retention needs 15 × 6 = 90 gallons, or 90 ÷ 7.48 ≈ 12 cubic feet — about a 2.3 ft cube. That is under a cubic yard, so it will compost cool and slow.
Frequently asked questions
How big does a compost pile need to be to heat up?
Roughly one cubic yard — a 3 × 3 × 3 ft heap. Below that the pile loses heat faster than it generates it and stays at ambient temperature, so it composts slowly and will not kill weed seeds or pathogens the way a hot pile does.
What is the right greens-to-browns ratio?
Aim for roughly equal volumes, or a bit more browns than greens. Too many greens turns the pile slimy and smelly; too many browns and it barely breaks down. Adjust by feel — add browns if it smells, add greens or water if it is dry and inert.
Will the bin overflow as I keep adding?
Usually not. Compost shrinks dramatically — often by half or more — as it decomposes, so finished material takes far less room than what you put in. Sizing for your retention period already accounts for the steady turnover.
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This calculator is for educational purposes. Double-check important results before acting on them.