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Worked Examples
- 1.Brown-to-green ratio: 15 / 5 = 3.0 (good)
- 2.Bin size: (5 + 15) x 8 / 40 = 4.0 cubic feet
- 3.Weeks to finish: 12 x (14 / 7) x (70 / 75) = 22 weeks
- 4.Annual waste diverted: (5 + 15) x 52 = 1,040 lbs
- 5.Annual CO2 saved: 5 x 52 x 0.34 = 88 lbs
A small household producing 20 lbs/week of compostable waste needs a 4 cubic foot bin and will have finished compost in about 22 weeks with weekly turning. This diverts 1,040 lbs of waste from landfills and saves 88 lbs of CO2 annually.
How to Size Your Compost Bin and Estimate Completion Time
Formula
Composting transforms kitchen scraps and yard waste into nutrient-rich soil amendment while diverting material from landfills. The key to effective composting is maintaining the right carbon-to-nitrogen ratio (ideally 25-30 parts brown to 1 part green by weight), adequate moisture, oxygen, and volume. A pile needs to be at least 3 cubic feet (27 cu ft) to generate enough internal heat for thermophilic decomposition.
Turning frequency and ambient temperature are the two biggest factors affecting composting speed. Frequent turning (every 3-7 days) introduces oxygen that aerobic microbes need, accelerating decomposition. Warmer temperatures (60-80 F) support faster microbial activity. Under optimal conditions, hot composting can finish in 8-12 weeks, while cold or passive composting may take 6-12 months.
Common use cases:
- Sizing a backyard compost bin
- Estimating when compost will be ready
- Tracking household waste diversion
- Reducing landfill methane emissions
Frequently Asked Questions
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