Calculator inputs
Example data table
A sample mix for quick reference (values are approximate).
| Finished volume | Shrink | Target C:N | Brown | Green | Estimated achieved C:N |
|---|---|---|---|---|---|
| 120 L | 30% | 30:1 | Dry leaves | Food scraps | ~29–33:1 |
| 4 cu ft | 25% | 28:1 | Straw | Grass clippings | ~26–30:1 |
| 200 L | 40% | 35:1 | Wood chips | Aged manure | ~33–38:1 |
Formula used
This tool treats each material as a wet mixture with three key properties: bulk density (kg/L), moisture fraction, and a C:N ratio.
- Dry mass = Volume × Density × (1 − Moisture)
- Carbon units ≈ Dry mass × CN/(CN+1)
- Nitrogen units ≈ Dry mass × 1/(CN+1)
- Mixture C:N = Sum(Carbon units) / Sum(Nitrogen units)
- The calculator solves a linear equation so that brown volume + green volume = remaining volume while meeting your target C:N as closely as possible.
This is an approximation. Shredding, airflow, and turning have major effects beyond C:N math.
How to use this calculator
- Enter the finished compost volume you want for your beds or pots.
- Pick a shrink allowance to estimate the starting pile size.
- Choose a brown and a green material, then adjust their properties if needed.
- Optionally add a small add-on (biochar, soil, or finished compost).
- Click Calculate mix to see recommended volumes and moisture advice.
- Layer and mix materials, then verify moisture by hand and adjust.
If the pile smells sour, add browns and turn. If it stays cold and dry, add greens and moisture.