Compost Ratio Calculator
Calculate the volume of brown materials (carbon) and green materials (nitrogen) needed for an ideal compost pile.
How to use this tool
- Enter the total target volume of your compost pile in cubic feet (3×3×3 ft = 27 ft³ is ideal).
- Enter the browns-to-greens ratio (3 is standard — 3 parts browns per 1 part greens).
- The calculator shows how many cubic feet of each material you need.
Balance your compost pile with the right ratio of brown (carbon) and green (nitrogen) materials.
⚠ This tool provides general estimates for education only and is not financial, tax or legal advice. Figures may not reflect your situation — verify with a qualified professional.
Formula
Total parts = browns-to-greens ratio + 1
Greens volume (ft³) = total pile volume ÷ total parts
Browns volume (ft³) = greens volume × browns-to-greens ratio
How it works
This calculator splits a target compost pile volume into its carbon-rich (browns) and nitrogen-rich (greens) components using the user-supplied volumetric ratio. The ratio represents how many parts of browns accompany each single part of greens.
A common recommendation is a 25–30:1 carbon-to-nitrogen ratio by mass; by volume a 3:1 browns-to-greens ratio is a practical approximation for typical garden materials. Actual decomposition speed depends on particle size, moisture (aim for 50–60%), and turning frequency.
Worked example
- Inputs: total pile volume 27 ft³, browns-to-greens ratio 3 (i.e., 3 parts browns : 1 part greens).
- Total parts = 3 + 1 = 4.
- Greens volume = 27 ÷ 4 = 6.75 ft³.
- Browns volume = 6.75 × 3 = 20.25 ft³.
Browns (carbon) volume = 20.25 ft³; greens (nitrogen) volume = 6.75 ft³.
Common mistakes to avoid
- Measuring browns and greens by weight rather than volume — the C:N ratio in composting is typically discussed by volume, and dense wet greens can throw off weight-based estimates.
- Using the 30:1 carbon-to-nitrogen ratio interchangeably with the browns-to-greens volume ratio — the two are not the same because different materials have different C:N ratios.
- Adding all the browns at once in a thick layer rather than alternating thin layers with greens, which slows decomposition significantly.
Key terms
- Browns (carbon materials)
- Dry, carbon-rich compost ingredients such as dry leaves, straw, cardboard, and wood chips that provide energy for decomposing microbes.
- Greens (nitrogen materials)
- Moist, nitrogen-rich materials such as grass clippings, fruit scraps, vegetable peels, and fresh plant trimmings that feed microbial populations.
- C:N ratio
- The carbon-to-nitrogen ratio by mass; an ideal compost pile targets approximately 25–30:1. A volumetric 3:1 browns-to-greens ratio is a practical field approximation.
- Hot composting
- An active composting method that maintains pile temperatures of 130–160°F through correct C:N balance, moisture, and regular turning, killing weed seeds and pathogens.
- Pile volume
- The total volume of all compost ingredients combined; a minimum of 1 cubic yard (27 ft³) is recommended to generate and retain enough heat for efficient decomposition.
Frequently asked questions
- What is the best browns to greens ratio for compost?
- The ideal carbon-to-nitrogen (C:N) ratio for active composting is 25–30:1. By volume, this translates to roughly 3 parts browns (leaves, straw, cardboard) to 1 part greens (grass clippings, food scraps, fresh plant material).
- What are examples of browns and greens?
- Browns (high carbon): dry leaves, straw, wood chips, cardboard, paper. Greens (high nitrogen): fresh grass clippings, vegetable scraps, coffee grounds, fresh plant trimmings.