♻️ Compost Ratio Calculator (C:N)
Add the materials in your compost pile and their proportions, and see the blended carbon-to-nitrogen ratio — with guidance to balance it.
| Material | C:N | Parts (by volume) | |
|---|---|---|---|
| 20:1 | |||
| 55:1 |
Blended C:N ratio
43:1
too woody (add greens)
A compost pile decomposes fastest around a carbon-to-nitrogen ratio of 25–30:1 — roughly 2–3 parts "browns" (carbon) to 1 part "greens" (nitrogen) by volume. This is a parts-weighted estimate; moisture and turning matter too. C:N values from composting-science references. 🔒 In your browser.
How the compost ratio calculator (c:n) works
Compost breaks down fastest when the carbon-to-nitrogen (C:N) ratio of the mix is around 25–35:1. Nitrogen-rich "greens" (food scraps, grass, manure) have a low C:N; carbon-rich "browns" (dry leaves, straw, cardboard) have a high one. The tool takes each material's typical C:N and your proportions and estimates the blended ratio, then tells you whether to add more greens or browns.
A rough rule of thumb is 2–3 parts browns to 1 part greens by volume. Too much nitrogen (a low ratio) makes a pile slimy and smelly; too much carbon (a high ratio) makes it break down very slowly. Moisture (like a wrung-out sponge) and turning for air matter just as much as the ratio.
Frequently asked questions
What is the ideal compost C:N ratio?
About 25–35 parts carbon to 1 part nitrogen (roughly 30:1) gives the fastest, cleanest decomposition. The finished compost settles nearer 10:1. This tool estimates your mix's ratio and flags if it's off.
What are greens and browns in composting?
"Greens" are nitrogen-rich, wetter materials — food scraps, grass clippings, coffee grounds, manure. "Browns" are carbon-rich, drier materials — dead leaves, straw, cardboard, wood chips. A good pile blends both.
What is the ratio of browns to greens?
Roughly 2–3 parts browns to 1 part greens by volume gets you into the ideal C:N range, because browns have a much higher carbon content per unit than greens have nitrogen. Adjust using the tool.
Why is my compost smelly or slimy?
Usually too much nitrogen (too many greens) and not enough air — a low C:N ratio going anaerobic. Mix in more browns (dry leaves, shredded cardboard) and turn the pile to add oxygen.
Why is my compost breaking down so slowly?
Often too much carbon (too many browns), too little nitrogen, or the pile is too dry. Add greens, ensure it's as moist as a wrung-out sponge, and turn it to introduce air.