Composting Calculator
Calculate compost bin capacity needed and estimate time to finished compost from inputs. Enter values for instant results with step-by-step formulas.
Reviewed by Daniel Agrici, Founder & Lead Developer
Formula
Bin Size = Total Volume x 1.2 | C:N = Total Carbon / Total Nitrogen
Bin size includes 20% extra for aeration. Composting time is estimated from a 12-week base adjusted for turning frequency, climate, and C:N ratio balance. Finished compost is approximately 45% of input volume.
Worked Examples
Example 1: Family of Four Weekly Composting
Problem:A family produces 20 liters of green waste (kitchen scraps) and 60 liters of brown waste (leaves, cardboard) weekly. They turn weekly in a temperate climate. What bin size and timeline?
Solution:Total volume = 20 + 60 = 80 liters\nC:N Ratio = (20 + 60) / (20/20 + 60/60) = 80 / 2 = 40:1 (slightly high, add more greens)\nRecommended bin = 80 x 1.2 = 96 liters minimum\nBase duration = 12 weeks x 0.8 (weekly turning) x 1.0 (temperate) x 1.3 (non-ideal C:N) = 12.5 weeks\nFinished compost = 80 x 0.45 = 36 liters
Result:96-liter bin needed | ~13 weeks to finish | 36 liters finished compost
Example 2: Large Garden Composting
Problem:A gardener has 50 liters of green waste and 150 liters of brown waste. They turn biweekly in a cold climate with a rectangular bin.
Solution:Total volume = 50 + 150 = 200 liters\nC:N Ratio = (50 + 150) / (50/20 + 150/60) = 200 / 5 = 40:1\nRecommended bin = 200 x 1.2 = 240 liters\nBase duration = 12 weeks x 1.0 (biweekly) x 1.5 (cold) x 1.3 (high C:N) = 23.4 weeks\nFinished compost = 200 x 0.45 = 90 liters
Result:240-liter bin needed | ~23 weeks to finish | 90 liters finished compost
Frequently Asked Questions
What is the ideal carbon to nitrogen ratio for composting?
The ideal carbon to nitrogen (C:N) ratio for efficient composting is between 25:1 and 35:1, with 30:1 being the sweet spot most experts recommend. Carbon-rich materials (browns) include dried leaves, cardboard, straw, sawdust, and newspaper. Nitrogen-rich materials (greens) include food scraps, fresh grass clippings, coffee grounds, and green plant trimmings. If the ratio is too high (too much carbon), decomposition slows dramatically because microorganisms lack the nitrogen needed for protein synthesis and reproduction. If the ratio is too low (too much nitrogen), the pile becomes anaerobic and produces foul ammonia odors. A practical rule of thumb is to maintain roughly 3 parts brown materials to 1 part green materials by volume.
How does composting work and what ratios should I use?
Composting decomposes organic matter through microbial activity. Aim for a carbon-to-nitrogen ratio of 25-30:1. Brown materials (leaves, cardboard, straw) provide carbon. Green materials (food scraps, grass clippings, manure) provide nitrogen. Keep moisture like a wrung-out sponge and turn every 1-2 weeks. Finished compost takes 2-6 months.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy