Compost Bin Size Calculator
Calculate compost bin size from weekly food scraps and yard waste.
Returns cubic feet needed for hot composting, cold composting, or vermicomposting.
Compost bin size is determined by how much organic waste you generate and the minimum volume needed for a pile to heat up, which kills weed seeds and pathogens and accelerates decomposition.
The Minimum Volume Rule:
A pile needs roughly 27 cubic feet, which is 0.76 m³ or about 765 litres, before its middle can hold 55–65 °C. That is the familiar 3 ft × 3 ft × 3 ft cube. Metric guides usually round it up to a tidy 1 m³, and the extra margin does no harm, but 27 cubic feet is the figure this calculator works to.
Smaller piles still compost. They just take 6–18 months and never get hot enough to kill weed seeds or pathogens, so keep diseased material and seeding weeds out of them.
Sizing from what you actually generate:
Bin volume = Weekly waste × Weeks to finish × 2
The factor of two is for the second pile. One batch is always sitting and finishing while you are still filling the next, so a single bin sized to exactly one batch is a bin you cannot use.
Household Waste Reference (kitchen scraps only, before any garden waste):
| Household Size | Weekly Kitchen Waste |
|---|---|
| 1–2 people | 5–10 litres (1.5–2.5 gal) |
| 3–4 people | 10–20 litres (2.5–5 gal) |
| 5–6 people | 20–35 litres (5–9 gal) |
Garden waste dwarfs kitchen waste for anyone with a lawn. A small garden adds roughly 15 litres a week across the season, a medium one 30, and a large one 55 or more, with most of it arriving in two spikes: grass in spring and leaves in autumn.
Worked Example:
A family of 4 with a medium garden: about 15 litres of kitchen waste and 30 of garden waste, so 45 litres a week. Hot composting, finishing in about 8 weeks.
45 × 8 × 2 = 720 litres
That is just under the 765-litre hot-composting minimum, so round up to a pair of 400-litre bays and run them in rotation. Two bays beat one big bin: you turn from one into the other, which does the mixing for you.
Standard Bin Sizes:
| Bin Type | Volume | Best For |
|---|---|---|
| Small plastic tumbler | 100–280 L | 1–2 person household, no hot composting |
| Standard open bin | 300–600 L | Small families |
| Twin-bay system | 2 × 500–800 L | Active hot composting |
| Windrow / large pile | 1,000+ L | Serious gardeners |
Practical Tips:
- The ideal Carbon:Nitrogen ratio is 25–30:1 — alternate brown (straw, cardboard) and green (food scraps, grass) layers
- Turn the pile every 1–2 weeks to add oxygen and speed decomposition
- A pile that doesn’t heat up needs more nitrogen (greens) or more moisture
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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