Composting Ratio Calculator
Balance greens and browns to hit the ideal carbon to nitrogen ratio for a compost pile.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
This model estimates brown material from entered C:N values and volumes. It treats volume as a proxy for comparable material amounts, but C:N is a mass ratio and bulk density and moisture differ by material. Use the result as a rough starting point, not a measured recipe; composting time also depends on moisture, oxygen, pile size and temperature.
Worked example
calculated with the default values below
Greens volume 5 gal · Carbon to nitrogen of the greens 15 C:N · Carbon to nitrogen of the browns 60 C:N · Target C:N for the pile 30 C:N · Pile width 3 ft · Pile height 3 ft Browns volume needed 9.53 gal · Pile volume 27.0 cu ft · Brown volume per green volume 1.91 gal/gal
General background references
Disclaimer
These are general gardening estimates. Planting windows, growth, water and nutrient needs vary by place and plant. Check local extension guidance and product labels before acting on an estimate.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
N=G÷(g+1); C=G×g÷(g+1); B=max(0,(t×N−C)÷(b÷(b+1)−t÷(b+1))); ratio=B÷G; pileVolume=w²×h
- G
- greens volume (gal)
- g
- greens C:N
- B
- browns volume (gal)
- b
- browns C:N
- t
- target C:N
- N
- green nitrogen proxy
- C
- green carbon proxy
- w
- pile width (ft)
- h
- pile height (ft)
rough volume-based starting point; C:N ratios are mass-based and material density and moisture vary, so this is not a measured recipe or timing estimate.
Frequently asked questions
What does the brown-per-green ratio mean?
It is the model’s estimated brown volume divided by the entered green volume. At the defaults it is about 0.95 gallons of browns per gallon of greens. Since C:N is a mass ratio and materials have different densities and moisture, this volume-based estimate is only a rough starting point; it does not predict when compost is finished.