Compost Ratio Calculator
Green:Brown
1:3
How it works
Compost requires the right ratio of carbon-rich browns to nitrogen-rich greens to decompose efficiently without odor. The Compost Ratio Calculator determines how many parts of each material to add to achieve the ideal carbon-to-nitrogen ratio.
**The ideal C:N ratio** Microorganisms work best at a C:N ratio of 25:1 to 30:1 by weight. Below 20:1 (too much nitrogen): compost smells like ammonia. Above 40:1 (too much carbon): decomposition is slow and the pile stays cool.
**Browns and greens** High-carbon browns: dry leaves (50:1), straw (80:1), cardboard (350:1), wood chips (400:1). High-nitrogen greens: grass clippings (20:1), food scraps (15:1), coffee grounds (20:1), fresh manure (10:1). Mix by weight, not volume — dry straw weighs much less than grass clippings.
**Volume to weight conversion** For practical home composting, approximate by volume: 2 to 3 parts browns to 1 part greens by volume works well. Add layers alternately and keep the pile as moist as a wrung-out sponge.
**Troubleshooting** Pile does not heat up: add nitrogen (greens), water, and turn to aerate. Pile smells: add carbon (browns) and turn to aerate. Pile is wet and slimy: add coarse browns like straw or wood chips and turn.
Privacy: all calculations run in the browser. No data is transmitted.
Frequently Asked Questions
- Bad smells indicate the wrong C:N ratio or insufficient aeration. Rotten egg smell (hydrogen sulfide): anaerobic (no oxygen) conditions — the pile is too wet and compacted, or has too much dense nitrogen material (grass clippings piled thick). Fix: turn the pile thoroughly, add coarse browns (wood chips, straw) to open the structure, and reduce watering. Ammonia smell: too much nitrogen (too many greens). Fix: add more browns (dry leaves, cardboard, straw) and turn to incorporate. No smell (no heat): insufficient nitrogen or moisture. Fix: add greens (kitchen scraps, fresh grass clippings) and water if dry. A healthy compost pile should smell like rich earth, not like anything else.
- Hot composting (maintained pile, regular turning): 4–8 weeks with active management. You need a minimum pile volume of 3×3×3 feet to generate enough heat to kill weed seeds and pathogens. Turn the pile every 3–5 days when the center temperature drops below 130°F (55°C). Cold composting (neglected pile, no turning): 6–18 months. Much less work but doesn't kill weed seeds or pathogens, so don't cold-compost diseased plant material or weed seed heads. Vermicomposting (worms): 2–3 months for kitchen scraps processed continuously. Commercial or tumbler composting: 4–6 weeks with correct ratios and regular turning.
- Meat, fish, and poultry: attract rodents and create odors. Dairy products and oils: same problem. Dog and cat feces: may contain human pathogens (Toxocara, Toxoplasma) that home composting temperatures may not eliminate. Diseased plant material: many plant diseases survive composting unless the pile reaches sustained 140°F+ temperatures. Weeds with seed heads: seeds survive in cool piles and re-infect your garden. Treated wood (pressure-treated, painted, stained): toxic to soil organisms. Black walnut leaves and wood: contain juglone, which inhibits growth of many plants. Citrus peels in large amounts: slow to break down and can repel worms in vermicomposting systems.
- No — they are complementary but different products. Topsoil is mineral soil (clay, silt, sand particles) with some organic matter. Compost is almost entirely organic matter in a stable, decomposed form. Finished compost is darker, lighter in weight, and has a higher nutrient concentration than topsoil. In the garden, use compost as an amendment (mixed into soil or used as mulch) rather than a replacement for soil — compost alone dries out too quickly in containers and has low density for proper root anchorage. A quality growing medium for raised beds combines compost (30–50% by volume) with soil or structural materials like vermiculite and peat moss.