Last Updated on September 18, 2026
Compost Ratio Calculator: Greens, Browns and C:N
A home compost pile works best around 30 parts carbon to 1 part nitrogen (30:1). Cornell Waste Management Institute and University of Missouri Extension both put the starting target near 30:1, dropping to about 10:1 once finished. Greens (grass clippings, kitchen scraps, manure) supply the nitrogen; browns (dry leaves, straw, cardboard, wood chips) supply the carbon. Pick your materials below to see your mix’s ratio, or use the solver to find how much of one to add to reach the target.
Carbon to nitrogen ratios by material
These are the values the calculator uses, mostly from University of Missouri Extension’s compost table. Where a source gives a range instead of one number, the calculator uses the midpoint, shown in the last column, since the ratio blends by volume in the arithmetic below.
| Material | Type | C:N ratio (source) | Value used | Source |
|---|---|---|---|---|
| Hog manure | Green | 5 to 7:1 | 6:1 | University of Missouri Extension |
| Poultry manure, fresh | Green | 10:1 | 10:1 | University of Missouri Extension |
| Kitchen scraps (vegetable wastes) | Green | 12 to 20:1 | 16:1 | University of Missouri Extension |
| Coffee grounds | Green | 20:1 | 20:1 | University of Missouri Extension |
| Grass clippings | Green | 12 to 25:1 | 18.5:1 | University of Missouri Extension |
| Fall leaves, dry | Brown | 50 to 67:1 | 58:1 | Missouri Extension (50) and Cornell Waste Management Institute (67) |
| Corn stalks | Brown | 60:1 | 60:1 | University of Missouri Extension |
| Straw | Brown | 40 to 100:1 | 70:1 | University of Missouri Extension |
| Paper or cardboard | Brown | 150 to 200:1 | 175:1 | University of Missouri Extension |
| Wood chips or sawdust | Brown | 200 to 500:1 | 350:1 | University of Missouri Extension |
The fall leaves row differs by source, so it’s a range: Missouri Extension’s own worked example uses 50:1, while Cornell Waste Management Institute publishes a measured sample of 0.75 percent nitrogen and 50 percent carbon, working out to 50 ÷ 0.75 = 66.67, rounded to 67:1. Whole branches and solid wood run much higher, up to 700:1 by Missouri’s figures, which is why shredding matters more than one “wood chips” row can show.
Compost ratio calculator
Enter what you have by 5-gallon bucket, standard 30-gallon lawn bag, or cubic foot (a bucket is about 0.67 cubic foot, a bag about 4). Leave anything unused blank.
Enter your materials above
Then press Calculate.
Worked example: fall leaves and kitchen scraps
Say you have 3 buckets of dry fall leaves (58:1) and 1 bucket of kitchen scraps (16:1). A bucket is about 0.67 cubic foot: 2.01 cubic feet of leaves, 0.67 of scraps. The combined ratio is a volume-weighted average, the method University of Missouri Extension describes for a mix (“average the ratios of the individual materials”):
| Material | Volume (cu ft) | C:N | Volume × C:N |
|---|---|---|---|
| Fall leaves | 2.01 | 58 | 116.6 |
| Kitchen scraps | 0.67 | 16 | 10.7 |
| Total | 2.68 | 127.3 |
127.3 ÷ 2.68 = about 47.5:1, well above the 30:1 target: 3 buckets of leaves against 1 bucket of scraps is still mostly carbon. To bring those leaves down to 30:1, solve for the unknown volume of scraps: 2.01 × (58 − 30) ÷ (30 − 16) = 2.01 × 28 ÷ 14 = 4.01 cubic feet, about 6 buckets.
So 3 buckets of dry leaves need roughly 6 buckets of scraps, not 1, to land near 30:1: browns carry far more carbon than greens are low in nitrogen, so it takes more greens by volume than most people expect. The solver above returns the same figure for the same numbers.
Worked example: grass clippings and leaves
University of Missouri Extension’s own illustration uses equal parts grass clippings and leaves: “a mixture of equal parts grass clippings and leaves might have a C:N of (20 + 50) ÷ 2 = 35.” That lands close to 30:1 with no adjustment, which is why grass and leaves are a common home pairing: neither is extreme, so roughly even proportions get you most of the way there.
Why the ratio matters
Too much nitrogen (mostly greens) and the pile can smell like ammonia or rotten eggs, and turn slimy instead of crumbly. Too much carbon (mostly browns) and there isn’t enough nitrogen to feed the microbes, so the pile barely heats up and can sit for a long time. Cornell Waste Management Institute frames it this way: below the target it will not heat up; above it, or if nitrogen is too concentrated, it can overheat and kill the organisms doing the work, or go anaerobic and smell. Decomposition is fastest somewhere in between.
Moisture and particle size
The ratio only works if the pile is also damp and broken into small pieces. Cornell Waste Management Institute notes moisture is often the more critical variable: a pile can have the right C:N ratio and still go anaerobic if too wet, or stall if too dry. A wrung-out sponge, damp but not dripping, is the usual target. Particle size matters too, since microbes work on surface area: whole cornstalks or branches break down far slower than chopped or shredded material, which is why Missouri Extension recommends shredding coarse material when possible.
A home pile doesn’t need to be exact
None of this needs a scale or a lab test. Cornell Waste Management Institute’s own guidance is to look up typical ratios in a published table, the approach this page uses, and it says the 30:1 target “may vary” with the material. Layering roughly equal-looking amounts of greens and browns, keeping the pile damp, and turning it occasionally gets most home piles into a workable range without any arithmetic. The calculator is for when a pile is stalling, smelling, or you want to check a mix before building it.
Finished compost improves what it’s spread on: the raised bed soil calculator figures how much a bed needs by volume, and Empty Raised Beds in Fall, Compost and Walk Away covers building a pile in an empty bed over winter. New to composting? Start with Composting for Beginners, or for a leaves-only route that skips balancing a ratio, How to Make Leaf Mold. The fall gardening checklist and leaving roots in when cutting spent crops are good places to gather materials, and spring bed prep is usually where finished compost gets used. More tools are on the charts and tools hub.
Quick questions
What is a good carbon to nitrogen ratio for compost?
About 30:1 to start. Cornell Waste Management Institute and University of Missouri Extension both give roughly 30 parts carbon to 1 part nitrogen as the starting target, dropping to near 10:1 once the compost is finished.
What happens if the compost ratio is too low in carbon?
Too much nitrogen can make a pile smell, turn slimy, or compact instead of staying crumbly. Adding more browns, like dry leaves, straw, or shredded cardboard, raises the ratio back toward the target.
What happens if the compost ratio is too high in carbon?
A pile that is mostly browns will not heat up well and can take a long time to break down, since there isn’t enough nitrogen to feed the microbes doing the decomposing. Mixing in more greens brings the ratio back down.
How many leaves per bucket of kitchen scraps for good compost?
Roughly the opposite of what feels intuitive: about twice as many scraps as leaves by volume. Using this page’s values, 3 buckets of dry leaves (58:1) need about 6 buckets of kitchen scraps (16:1) to land near 30:1.
Does a home compost pile need an exact C:N ratio?
No. Cornell Waste Management Institute notes the 30:1 target can vary with the material, and roughly layering greens and browns while keeping the pile damp gets most home piles into a workable range without any measuring.
Let the planner place them
Plan My Garden is free to start: enter your zip code and it finds your frost dates, draw your beds, pick what you want to grow, and it places each plant at square-foot spacing and builds a planting schedule from those dates.
Related: Composting for Beginners · How to Make Leaf Mold · Empty Raised Beds in Fall, Compost and Walk Away · Raised Bed Soil Calculator · Fall Gardening Checklist · Leave the Roots In When You Cut Spent Crops · Spring Garden Prep · Charts and Tools
