Composting Calculator

The ideal C:N ratio for active composting is approximately 25:1 to 30:1. This balance allows heat-loving (thermophilic) microbes to thrive, driving your pile to temperatures of 130–160°F and speeding up decomposition. Ratios that are too high (too much carbon) slow the process, while ratios that are too low (too much nitrogen) can cause ammonia release and bad odors.

Green materials are nitrogen-rich and typically moist — these include food scraps, grass clippings, fresh plant trimmings, and manure. Brown materials are carbon-rich and typically dry — these include dead leaves, cardboard, straw, and wood chips. A good compost pile needs roughly equal volumes of each category to achieve the ideal C:N ratio.

Compost typically shrinks 40–60% from its original volume as organic matter breaks down, moisture evaporates, and microbes consume carbon. A pile that starts at 10 cubic feet will often yield around 4–6 cubic feet of finished compost. The exact reduction depends on moisture levels, aeration, temperature, and material types.

Active hot composting with the correct C:N ratio and regular turning can produce finished compost in as little as 4–8 weeks. Passive cold composting, where a pile is left mostly undisturbed, may take 6 months to 2 years. Regular turning, maintaining moisture at 40–60%, and achieving the right C:N balance all accelerate the process.

Avoid adding meat, fish, dairy products, oily foods, pet waste (from cats or dogs), diseased plants, and treated wood. These materials can attract pests, create foul odors, introduce pathogens, or introduce harmful chemicals into your finished compost. Stick to fruit/vegetable scraps, yard waste, coffee grounds, and plain paper products.

Yes, with adjustments. Worm bins (vermicomposting) thrive at a slightly lower C:N ratio of around 20:1, as worms prefer a moister, less carbon-heavy environment. Avoid adding citrus, onions, and spicy foods in worm bins. The volume estimates still apply, though worm castings are denser and shrink differently than traditional hot compost.

This calculator provides a reasonable approximation based on average bulk densities and typical C:N ratios for each material type. Real-world results will vary depending on particle size, moisture content, how finely materials are shredded, turning frequency, and seasonal temperatures. Use the results as a planning guide rather than a precise measurement.

If your C:N ratio is too high (too much carbon), add more nitrogen-rich greens such as fresh grass clippings, food scraps, or a small amount of blood meal or manure. If your ratio is too low (too much nitrogen), add more carbon-rich browns like dry leaves, shredded cardboard, or straw. Aim for the 25–30:1 sweet spot for optimal decomposition.