What Is a Compost Carbon-Nitrogen Ratio Calculator?
Every compost ingredient has a rough carbon-to-nitrogen (C:N) ratio — dry, woody "browns" are carbon-heavy, and fresh, wet "greens" are nitrogen-heavy. Composting microbes work fastest around a 25:1 to 35:1 blended ratio. This calculator mass-weights two ingredients' typical C:N ratios to estimate where your mix lands, and whether to add more browns or greens.
Getting this ratio roughly right is the single biggest factor in whether a compost pile breaks down quickly and stays odor-free, or sits soggy and slow for months.
How to Read Your Results
Blended C:N Ratio
Your mix's estimated overall carbon-to-nitrogen ratio, weighted by how much of each ingredient you added.
Ideal Target Range
Most composting guides target roughly 25:1 to 35:1 — inside that band, decomposition is typically fast and the pile shouldn't smell.
Suggested Adjustment
If your blend is outside the ideal range, this tells you whether to add more carbon-rich browns or nitrogen-rich greens to rebalance it.
Real-World Example
10 lb of dry leaves (about 60:1) mixed with 20 lb of fresh grass clippings (about 20:1):
| Ingredient | Amount | C:N Ratio |
|---|---|---|
| Dry leaves | 10 lb | 60:1 |
| Grass clippings | 20 lb | 20:1 |
| Blended ratio | 30 lb total | 33.3:1 |
That combination lands right in the ideal 25:1–35:1 range, so this pile should compost efficiently without extra adjustment.
Tips for a Healthy Compost Pile
- Layer, don't just dump. Alternating thin layers of browns and greens mixes more evenly than one big pile of each.
- Moisture matters too. Aim for the texture of a wrung-out sponge — too dry slows microbes, too wet can go anaerobic and smell.
- Turn the pile every week or two to add oxygen and speed decomposition.
- When in doubt, add browns. A pile that's too carbon-heavy just composts slowly; one that's too nitrogen-heavy can smell and attract pests.
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Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team