Compost Ratio Calculator
Calculate the carbon-to-nitrogen ratio for your compost pile and get recommendations for perfect compost.
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How to use this calculator
Weighted average C:N = (sum of each material's kg × its C:N ratio) / total kg. Ideal C:N ratio is 25–30:1 for active decomposition.
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Select your brown (carbon-rich) material and enter its weight in kg.
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Select your green (nitrogen-rich) material and enter its weight in kg.
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Read the estimated C:N ratio and check if it falls in the ideal 25–30:1 range.
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Follow the recommendation to adjust your mix for faster, better compost.
Frequently asked questions
What is the ideal C:N ratio for composting?
A ratio of 25–30:1 (25 to 30 parts carbon for every 1 part nitrogen by weight) gives compost microbes the balanced diet they need to decompose material efficiently. Too much carbon slows decomposition; too much nitrogen creates a smelly, slimy pile.
Why does cardboard have such a high C:N ratio?
Cardboard is nearly pure cellulose with very little nitrogen, giving it a C:N ratio of around 400:1. A small amount of cardboard goes a long way to raising the ratio. Always shred or tear cardboard into small pieces and remove tape and glossy coatings before adding to the pile.
How do I speed up composting?
Turn the pile every 1–2 weeks to aerate it, keep moisture levels similar to a wrung-out sponge, shred materials into small pieces, and maintain an ideal C:N ratio of 25–30:1. A well-managed pile can produce finished compost in 4–8 weeks.
Compost Ratio Calculator — C:N Ratio for Perfect Compost
The Carbon-to-Nitrogen Ratio Explained
Compost microorganisms need carbon for energy and nitrogen for protein synthesis. A C:N ratio of 25–30:1 keeps microbial activity high and compost temperatures elevated (50–65°C), which kills weed seeds and pathogens. A pile that is too carbon-rich decomposes slowly; too nitrogen-rich produces ammonia odours.
Common Brown vs Green Materials
Browns (high carbon): dry leaves, cardboard, straw, wood chips, newspaper. Greens (high nitrogen): grass clippings, food scraps, fresh manure, coffee grounds, fresh plant trimmings. Alternate layers of each to build a balanced pile from the start.
Signs Your Compost Pile Is Off-Balance
A pile that smells like ammonia has too much nitrogen — add more browns and turn. A pile that is dry and not heating up has too much carbon — add more greens and water. A well-balanced pile smells earthy and reaches temperatures of 50–65°C within 3–5 days of turning.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →