What this calculator works out
This calculator estimates the compost bin capacity a household needs, combining an allowance per person for kitchen waste with an allowance per square metre of garden.
Both figures are rules of thumb. The garden allowance dominates for most properties, because grass clippings and prunings vastly outweigh kitchen scraps by volume.
Enter your details
Before you choose a bin
- Garden size means the planted and grassed area that generates waste, not the total plot including the house and drive.
- The waste factor is litres per square metre per year. A closely mown lawn with hedges produces more than a low-maintenance gravel garden.
- Compost reduces to roughly a third of its original volume as it decomposes, so a bin handles more input than its capacity suggests.
- Two smaller bins usually work better than one large one, because you can fill one while the other matures.
Composting needs a rough balance of nitrogen-rich green material — grass, kitchen waste, soft prunings — and carbon-rich brown material such as cardboard, dead leaves and woody stems. Roughly equal volumes is the usual guidance. A bin of grass alone turns to slime; a bin of woody material alone barely breaks down.
How this calculator works
Two allowances added together:
Capacity in litres = (people × 60) + (garden area × waste factor)The 60 litres per person is an annual allowance for kitchen waste. The garden term uses whatever waste factor you enter, so it can be adjusted for how much material the garden actually produces.
Because material shrinks substantially as it decomposes, a bin can accept considerably more input over a year than its stated capacity — which is why the result should be read as a starting point rather than a limit.
Worked example: four people, 100 m² of garden
Using the default figures — four people, 100 m² of garden, a waste factor of 1.2:
- Kitchen allowance: 4 × 60 = 240 litres
- Garden allowance: 100 × 1.2 = 120 litres
- Total: 360 litres
360 litres is roughly one and a half standard plastic compost bins, which typically hold 220 to 330 litres. Two 220 litre bins would be the practical answer — and the better one, because you can stop adding to a full bin and let it finish while filling the second.
Common mistakes
- Buying one large bin instead of two smaller ones. You need somewhere for material to mature undisturbed.
- Filling a bin with grass alone. It compacts and goes anaerobic; mix in brown material.
- Siting a bin in deep shade. Warmth speeds decomposition considerably.
- Adding cooked food or meat to an open bin. It attracts rats; use a sealed system for those.
- Never turning the heap. Turning is not essential but roughly halves the time.
Frequently asked questions
How long does compost take?
Six months to two years, depending on the mix, the temperature and whether the heap is turned. A well-balanced heap turned regularly in summer can produce usable compost in three to six months. An untouched heap of mixed material takes a year or more, which is fine if you have space to leave it.
What can and cannot go in?
In: fruit and vegetable peelings, tea leaves, grass clippings, soft prunings, dead leaves, cardboard, paper, egg shells. Not in an open bin: cooked food, meat, fish and dairy, which attract rodents, and perennial weed roots or seeding weeds unless the heap gets genuinely hot. Pet waste from meat-eating animals is generally excluded.
Do I need a hot bin?
Not for ordinary garden composting. Insulated hot composting systems reach temperatures that kill weed seeds and pathogens and can process cooked food, and they work much faster — at considerably higher cost. For most gardens a standard bin and patience is adequate.
Why is my compost slimy or smelly?
Too much green material, too wet, and not enough air. Mix in cardboard, dead leaves or woody prunings, and turn the heap to introduce air. A properly balanced heap smells earthy rather than sour.
Is what I enter stored?
No. Household and garden figures are processed in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — household waste, composting and garden waste collection guidance
- Royal Horticultural Society — composting advice, including what to add and how to manage a heap
Sources are checked at publication and can change — how I choose and check references.