Compost Bin Volume & Output Calculator

Home Composting Guide

What do I need to know about Compostable Materials?

GREENS (high nitrogen, fast-rotting): grass clippings. Vegetable peelings. Fruit waste. Coffee grounds and used tea leaves (NOT teabags with plastic). Cut flowers, deadheads. Fresh weeds (not seed heads or perennial weeds). Plant prunings. BROWNS (high carbon, slow-rotting): cardboard (torn into small pieces). Newspaper and shredded paper. Dry leaves. Twigs and small branches. Egg shells. Wood ash (small amounts). Straw or hay. AVOID: cooked food, which attracts rats unless using a hot composter. Meat, dairy, and cooked food generally, since these attract pests and produce unpleasant smells in a standard cold composting system.

What should I know about The Brown:Green Ratio?

Ideal C:N ratio: approximately 30:1. Translates roughly to 2-3 parts brown to 1 part green by volume. Common problem: too much green (slimy, smelly compost). Add more brown — shredded cardboard works immediately. Too much brown (slow, dry compost). Add more green or water. Layering or mixing: traditional layered approach (alternating browns and greens) works. Mixing as you add also fine. Aim for moisture like a wrung-out sponge — squeeze a handful, should clump but not drip. Turning the heap introduces oxygen, which speeds up decomposition significantly — a heap turned regularly can finish in months rather than the year or more an untouched heap might take.

What should I know about Bin Sizing?

Approximate annual compostable waste: kitchen waste only: 70 kg/person/year. Plus garden waste: typical 50m² lawn = 200 kg/year cuttings. Larger garden with prunings: 500-1500 kg/year. Bin volume: 200-300L sufficient for small household + small garden. 400L (single Dalek bin): typical 4-person household + medium garden. 600L+: large garden producers. 1000L+: 2-3 bay wooden system for allotments. Compost shrinks dramatically — final compost is approximately 20% of original input volume. Two-bin systems let you keep filling one bin while the other finishes composting, which is more practical than a single bin for most regular composters.

What do I need to know about Hot Composting?

Hot composters (HotBin, Joraform, Aerobin): insulated bins reaching 60-70°C internal temperature. Bacterial action accelerates dramatically. Benefits: 30-90 days to finished compost (vs 12-18 months traditional). Kills weed seeds and pathogens. Compost cooked meat, fish, dairy (excluded from cold systems). Cost: £200-500 for serious hot composters. Worthwhile for: small gardens with limited space. Households producing food waste from cooking. People wanting compost quickly. Caveats: requires active management — regular turning and monitoring temperature — which is more effort than passive cold composting but produces usable compost in weeks rather than a year.