Compost C:N Ratio Chart
Carbon-to-nitrogen ratios, moisture, and bulk density for 53 common composting materials — the same cited dataset behind the C:N Ratio Calculator, laid out as a browsable chart.
The carbon-to-nitrogen ratio — written C:N — is the single most useful number for balancing a compost pile. It compares how much carbon a material holds against its nitrogen, by dry weight. Microbes need both: nitrogen to build their bodies and carbon for energy. When the overall mix lands near 25–35:1, they multiply fast and the pile heats.[1] Too much nitrogen (a low ratio) and the excess gases off as ammonia — that sharp smell from a pile of pure grass clippings. Too much carbon (a high ratio) and decomposition stalls for lack of nitrogen to work with.
Every value on this chart is a typical figure with a minimum-to-maximum range, because real materials are not fixed. Grass clippings off a fertilized lawn carry far more nitrogen than clippings from a neglected one; autumn leaves vary by tree species; cardboard shifts with bleaching and printing. The composting literature itself disagrees on many of these numbers, and where it does we show the spread rather than pretend to a single answer — the same approach documented on the methodology page.[2] Use the typical column for planning and the range to understand how much a material can drift.
Two other columns matter when you build a pile by volume rather than by weight. Moisture is listed because C:N is a dry-weight figure: a bucket of fresh grass is mostly water, so it delivers less actual carbon and nitrogen than the ratio alone implies. Bulk density — weight per unit volume, toggling between US and metric with the switch in the header — lets you translate the wheelbarrows and buckets you actually measure into the dry mass the C:N math needs. The C:N Ratio Calculator does that conversion for you; this chart is the lookup table behind it.
As a fast rule of thumb, scan the C:N column: materials under about 30:1 behave as nitrogen-rich greens (food scraps, fresh grass, manures) that fuel the heat, and materials well above 30:1 behave as carbon-rich browns (dry leaves, straw, paper, wood) that add structure and soak up moisture. A working pile blends the two. For which materials belong in a pile at all, see what you can and can't compost.
Food & Kitchen Scraps
Kitchen and food-prep waste. Most of these are wet, nitrogen-rich "greens" with a low C:N — fast to break down but prone to odor and pests, so bury them in the pile and balance with browns. Meat, fish, and dairy are listed for reference, but belong out of a typical home pile.
| Material | C:N ratio | Moisture | Bulk density | Notes & prep |
|---|---|---|---|---|
| Mixed food scraps / kitchen waste | 20:1 (15–25) | 70% | 42 lb/ft³ | Varies widely by composition. Fruit-heavy kitchen scraps pull moisture higher. |
| Fruit waste (fresh) | 28:1 (20–35) | 82% | 42 lb/ft³ | High moisture; effective C:N lower on wet basis. Citrus peels on higher end of C:N. |
| Vegetable scraps (mixed) | 15:1 (11–19) | 78% | 42 lb/ft³ | Leafy greens pull ratio down. Starchy vegetables (potato peels) pull higher. |
| Coffee grounds (used) | 22:1 (20–24) | 60% | 42 lb/ft³ | Often cited at 20:1; behave as a 'green' despite brown color. Dense and wet. |
| Bread / grains | 50:1 (45–60) | 40% | 30 lb/ft³ | High carbohydrate, moderate N. Can attract pests — bury in center of pile. |
| Meat / fish scraps | 4:1 (3–5) | 70% | 42 lb/ft³ | Very high N; odor concern; not recommended for home piles. Attracts pests. |
| Dairy products | 5:1 (4–6) | 80% | 50 lb/ft³ | Very high N; odor concern; not recommended for home piles. |
| Eggshells | 300:1 (200–400) | 10% | 30 lb/ft³ | Negligible C and N in practical quantities; calcium source only. C:N not meaningful — very high ratio used to indicate minimal nutrient contribution. |
Yard & Garden Waste
Grass, leaves, prunings, straw, and other garden material. This group spans the full range: fresh green clippings behave as nitrogen-rich greens, while dry autumn leaves and straw are carbon-rich browns. The same material shifts C:N dramatically as it dries.
| Material | C:N ratio | Moisture | Bulk density | Notes & prep |
|---|---|---|---|---|
| Grass clippings (fresh, green) | 17:1 (9–25) | 80% | 20 lb/ft³ | Lower C:N for heavily fertilized lawns; higher end for unfertilized. Spring clippings have higher moisture. Sources vary: 12:1–25:1. |
| Grass clippings (dry/brown) | 60:1 (45–80) | 15% | 6 lb/ft³ | Dried and yellowed; significantly higher C. Behaves as a 'brown.' |
| Leaves (fresh, green) | 25:1 (20–30) | 40% | 11 lb/ft³ | Varies by species. Fall green leaves before color change. |
| Leaves (dry, autumn/fallen) | 60:1 (40–80) | 15% | 3 lb/ft³ | Wide species variation. Mixed deciduous default ~60:1. Oak and beech on higher end (60–85:1); ash and walnut lower (25–45:1). Shredding recommended. |
| Straw (wheat / oat) | 100:1 (50–150) | 15% | 4 lb/ft³ | Wide range cited; some sources say 75:1–150:1. Lower density when loose, higher when baled. High C; requires high-N materials. |
| Straw (rice) | 125:1 (100–150) | 13% | 3 lb/ft³ | More resistant lignin than wheat straw; slow breakdown. Requires shredding. |
| Hay (general / grass hay) | 25:1 (20–30) | 20% | 7 lb/ft³ | Legume hay (alfalfa) on lower end (15:1); grass hay higher. May contain weed seeds. |
| Alfalfa hay | 14:1 (13–15) | 18% | 7 lb/ft³ | High N content; excellent activator. Can be used in place of manure. |
| Garden trimmings (mixed green) | 25:1 (20–30) | 60% | 18 lb/ft³ | Herbaceous annuals and perennials. Chop or shred for faster decomposition. |
| Hedge trimmings (woody) | 45:1 (30–60) | 50% | 22 lb/ft³ | Higher C with more woody material. Chipping dramatically accelerates decomposition. |
| Corn stalks | 60:1 (50–75) | 70% | 8 lb/ft³ | Resistant cellulose; slow breakdown. Shred or chip for best results. |
| Pine needles | 80:1 (60–110) | 15% | 5 lb/ft³ | Very slow breakdown due to wax coating and high lignin. Slight acidifying effect; beneficial for acid-loving plants. Mix sparingly. |
| Weeds (green, non-seeding) | 18:1 (15–20) | 72% | 18 lb/ft³ | Similar to grass clippings. Avoid weeds with seed heads or perennial roots unless hot-composting (>131°F for 3+ days). |
| Seaweed (fresh) | 12:1 (5–19) | 82% | 45 lb/ft³ | High N; salty — rinse thoroughly before composting to avoid salt damage. High mineral content; excellent activator. |
| Seaweed (dried / kelp meal) | 20:1 (15–25) | 15% | 30 lb/ft³ | Dried seaweed; iodine trace; use sparingly. Rich in micronutrients. |
Paper & Cardboard
Uncoated paper and cardboard are high-carbon browns that add structure and soak up excess moisture. Shred and moisten them so they do not mat into airless layers, and skip anything glossy, waxed, or heavily inked.
| Material | C:N ratio | Moisture | Bulk density | Notes & prep |
|---|---|---|---|---|
| Newspaper (black ink, plain) | 185:1 (170–200) | 7% | 25 lb/ft³ | Very high C; lignin-bound cellulose — slow breakdown. Shred or tear into strips. Avoid glossy/color-printed paper. |
| Office paper (white / copy paper) | 175:1 (150–200) | 6% | 25 lb/ft³ | Similar to newspaper. Shred for faster decomposition. |
| Shredded paper (mixed office) | 175:1 (150–200) | 6% | 5 lb/ft³ | Shredding dramatically accelerates breakdown. Very low bulk density when loose. |
| Cardboard (corrugated, plain) | 300:1 (150–500) | 10% | 8 lb/ft³ | Wide range cited due to corrugation, bleaching, and inks. Shred or tear; remove tape. Do NOT use wax-coated cardboard. |
| Paper bags (brown kraft) | 140:1 (100–175) | 7% | 15 lb/ft³ | Tear into pieces for faster breakdown. |
| Paper towels / tissues (unbleached) | 140:1 (110–175) | 8% | 4 lb/ft³ | Acceptable if not heavily soiled with cleaning chemicals. Unbleached preferred. |
Manures
Herbivore manures are nitrogen-rich activators. Their C:N depends heavily on how much bedding is mixed in — sawdust bedding pushes the ratio far higher than straw. Age or hot-compost manure before applying it to food crops.
| Material | C:N ratio | Moisture | Bulk density | Notes & prep |
|---|---|---|---|---|
| Chicken manure (fresh, no bedding) | 7:1 (5–10) | 65% | 55 lb/ft³ | Very hot; use sparingly or blend with high-C materials. Can burn plants if applied fresh. |
| Chicken manure (with bedding/litter) | 20:1 (15–25) | 35% | 35 lb/ft³ | Bedding type heavily affects ratio. Wood shavings pull C:N higher; straw lower. |
| Chicken manure (composted) | 13:1 (11–15) | 40% | 30 lb/ft³ | Partially stabilized; safer for direct application than fresh. |
| Cow manure (fresh) | 18:1 (15–25) | 80% | 58 lb/ft³ | Some sources cite 11:1–30:1. Very wet; may need dry carbon material to balance moisture. |
| Cow manure (aged / dried) | 14:1 (10–18) | 45% | 38 lb/ft³ | Lower moisture than fresh; some N loss during aging. |
| Horse manure (fresh, no bedding) | 30:1 (25–35) | 65% | 28 lb/ft³ | Varies with feed type. High-grain diet produces lower C:N. |
| Horse manure (with straw bedding) | 45:1 (30–60) | 60% | 28 lb/ft³ | Common backyard scenario. More straw = higher C:N. |
| Horse manure (with sawdust bedding) | 80:1 (60–100) | 55% | 22 lb/ft³ | Sawdust dramatically raises C:N. Requires significant N-rich amendment to balance. |
| Rabbit manure (fresh) | 6:1 (4–8) | 52% | 35 lb/ft³ | Very high N; cold compost safe — can be applied directly to soil without hot composting. |
| Pig manure (fresh) | 10:1 (5–15) | 78% | 55 lb/ft³ | Pathogen concern — requires hot composting (>131°F for 3+ days). Not recommended for home piles without proper management. |
| Sheep / goat manure (fresh) | 18:1 (13–22) | 68% | 28 lb/ft³ | Dry pelleted form is easy to handle. Higher N than cattle manure. |
Wood Products
Sawdust, chips, and bark are the highest-carbon materials on this chart — slow to break down and capable of temporarily tying up nitrogen. Use them in thin layers or for structure, and never compost treated, painted, or stained wood.
| Material | C:N ratio | Moisture | Bulk density | Notes & prep |
|---|---|---|---|---|
| Sawdust (fresh / green) | 400:1 (200–750) | 40% | 28 lb/ft³ | Extreme C:N range depending on species and freshness. Can cause N immobilization — balance with very high N materials. Avoid cedar or treated wood. |
| Sawdust (kiln-dried) | 500:1 (300–750) | 10% | 16 lb/ft³ | Very dry; very high C. Requires abundant moisture and N to compost. |
| Wood chips (fresh, mixed species) | 300:1 (200–400) | 50% | 28 lb/ft³ | Particle size critically affects decomposition rate. Smaller chips (1/2") break down far faster than large chunks. |
| Wood chips (aged / weathered) | 150:1 (100–200) | 30% | 22 lb/ft³ | Some N immobilization has occurred. Lower C:N than fresh. Partially colonized by fungi. |
| Bark (shredded / mulch) | 150:1 (100–200) | 40% | 28 lb/ft³ | Varies by species. Higher in tannins than wood chips — can slow decomposition. |
| Branches / twigs (chipped) | 100:1 (50–150) | 45% | 22 lb/ft³ | Depends on bark-to-wood ratio and species. Chipping to <1" accelerates breakdown significantly. |
Miscellaneous & Specialty
Less-common feedstocks. Some are potent nitrogen activators (blood meal, feathers, hair, wool) that break down slowly despite their low C:N; others are byproducts such as spent brewing grain, coffee chaff, and spent mushroom substrate.
| Material | C:N ratio | Moisture | Bulk density | Notes & prep |
|---|---|---|---|---|
| Human hair | 4:1 (3–6) | 15% | 4 lb/ft³ | Very high N but extremely slow breakdown due to keratin protein structure. Chop or soak to accelerate. |
| Wool (raw fiber) | 6:1 (5–8) | 15% | 5 lb/ft³ | High N but slow breakdown. Shred or pull apart to increase surface area. |
| Feathers | 4:1 (3–5) | 15% | 3 lb/ft³ | High N; slow breakdown due to keratin. Bury in pile to reduce odor. |
| Blood meal | 3.5:1 (3–4) | 8% | 50 lb/ft³ | Extremely high N activator. Use very sparingly — can burn plants if over-applied. Strong odor. |
| Coffee chaff (roaster chaff) | 30:1 (25–35) | 8% | 5 lb/ft³ | Light, dry material from coffee roasting. Good carbon amendment; breaks down moderately fast. |
| Spent brewing grain (wet) | 8:1 (5–12) | 75% | 50 lb/ft³ | Very wet and high N. Mix with dry carbon materials immediately to prevent anaerobic decomposition. |
| Spent mushroom substrate | 50:1 (30–75) | 65% | 30 lb/ft³ | Varies widely by original substrate (straw, sawdust, grain, etc.). Already partially broken down by fungi. |
Frequently Asked Questions
Why does this chart show a range of C:N values instead of one number?
Because a material's carbon-to-nitrogen ratio genuinely varies. Grass clippings from a fertilized lawn run lower than clippings from an unfertilized one; dry leaves vary by tree species; cardboard varies with bleaching and inks. The chart lists a typical value for planning and a min-to-max range so you can see how much a material shifts with freshness, species, and moisture.
Are these carbon-to-nitrogen ratios measured wet or dry?
The C:N ratios are on a dry-mass basis, the standard way composting references report them. That's why moisture is a separate column: a wet material like fresh grass contributes less dry carbon and nitrogen per bucketful than its C:N alone suggests. The C:N Ratio Calculator combines the dry-mass ratio, moisture, and bulk density to work out a blend by volume.
How do I tell a green from a brown using this chart?
Look at the C:N column. Materials below roughly 30:1 act as nitrogen-rich greens — food scraps, fresh grass, and manures that heat a pile. Materials well above 30:1 act as carbon-rich browns — dry leaves, straw, paper, and wood that add structure and absorb moisture. A good pile blends the two toward an overall 25 to 35:1.
Can I download the compost feedstock dataset?
Yes. The full dataset is published as JSON at /data/feedstocks.json under a Creative Commons Attribution 4.0 license, so you can reuse it with credit. It includes the minimum, typical, and maximum C:N ratio, moisture, and bulk density for every material, plus the source citation for each entry.