What is the ideal C:N ratio for compost?

About 25–30:1 carbon to nitrogen by our target band. A common field heuristic is two to three parts browns to one part greens by volume — then check the mix against feedstock ratios in the calculator (the parts rule itself is not a separate constant).

Why does my compost pile smell bad?

Usually too many greens (low C:N) and/or too wet. Add dried leaves or straw (browns) and turn. A healthy pile smells like a forest floor, not ammonia or rot.

How much finished compost do I get?

We plan finished volume at about one-third of the starting pile. A 30 cu ft pile yields about 10 cu ft finished — useful for top-dressing beds.

What counts as greens vs browns?

Greens (lower C:N): grass clippings 17, food scraps 15, fresh manure 15. Browns (higher C:N): dried leaves 60, straw 80, wood chips 400, shredded cardboard 350.

Compost C:N Ratio Explained (Without the Chemistry Degree)

C:N sounds like a lab coat. In the pile it just means balance carbon-rich browns with nitrogen-rich greens so microbes can heat, eat, and finish. Our target band is 25–30:1. Below that the pile goes soggy and sharp-smelling; above it, the heap sits cold and lazy. The compost calculator averages the materials you add and tells you whether to throw on grass or leaves.

The feedstock table (our numbers)

Material	Role	C:N
Food scraps	Green	15
Fresh manure	Green	15
Grass clippings	Green	17
Dried leaves	Brown	60
Straw	Brown	80
Shredded cardboard	Brown	350
Wood chips	Brown	400

Bucket rule of thumb: start around 2–3 volumes of browns per 1 volume of greens, then check with the ratios. Equal volumes of leaves (60) and grass (17) average (60+17)/2 = 38.5 — still a bit brown in our advice engine (wants more greens). Two parts leaves + one part grass → (120+17)/3 ≈ 45.7 — also “more greens.” That is why “I only add leaves” piles nap until August.

How the calculator thinks

We use a volumetric weighted average: sum(C:N × volume parts) ÷ total parts. It is a teaching approximation, not a laboratory mass balance, and it is good enough to steer a backyard heap.

Advice bands:

Below 25: more browns (leaves, straw, cardboard)
25–30: on target
Above 30: more greens (grass, scraps, manure)

Wood chips at 400 are powerful browns — great for structure, easy to overshoot. Chip-heavy piles need greens and time; they are not a one-week hot recipe.

Hot, warm, and cold realities

A pile that is at least about a cubic yard (common hot-compost practice — not a constant in our C:N file), watered like a wrung sponge, and turned when it cools will heat. Smaller kitchen crocks still compost; they just finish slower and rarely hit the textbook hot-compost kill zone for seeds and pathogens.

Finished volume in our data is about ⅓ of what you started with. Plan fills accordingly: if you need 10 cu ft of finished compost for beds, start nearer 30 cu ft of raw mix — then confirm bed top-dress needs with the raised bed soil calculator or the soil amendment calculator.

Troubleshooting smells and stalls

Ammonia or rotten smell: too green and/or anaerobic (wet, compacted). Fork in leaves or straw, add coarse sticks for air, turn, and ease off the hose.

Nothing happening: too brown, too dry, or too small. Add greens, moisture, and mass. Chop materials finer.

Slimy layers of grass: grass at 17 mats into a seal. Mix thin layers with leaves; never dump a lawn bag as a single stratum.

Ant or fly parties: bury food scraps in the hot center; cover with browns. Skip meat and oils in casual backyard piles if pests are already winning.

Weed seeds everywhere: the pile never got hot enough. Screen finished compost or keep weed seed heads out of cold heaps.

Manure notes

Fresh manure sits at C:N 15 in our table — a strong green. Hot-compost it with plenty of browns. For food gardens, follow food-safety guidance on raw-manure intervals (commonly discussed as on the order of 90–120 days before harvest depending on crop contact — defer to current extension/USDA guidance, not a number invented here). Composting manure first is the neighbor-friendly path.

Chicken manure is potent; pair it with carbon or you will smell why.

Building a no-drama recipe

A practical starter mix for many yards:

Save fall leaves (60) in bags or a bin.
Add kitchen scraps (15) weekly, buried.
Layer thin grass (17) when you mow — never a foot-thick wet blanket.
Keep moisture even; turn every week or two if you want speed (chore cadence, not a data-file constant).
When the calculator says you are above 30, add a scoop of grass or manure; when below 25, add leaves.

Straw (80) is the tidy brown if leaves run out. Cardboard (350) works shredded; glossy or tape-heavy board is junk.

Using the finished product

Screen chunky bits back into the next pile. Use finished compost to:

Blend Mel’s mix thirds for new raised beds
Top-dress established beds an inch at a time
Multiply microbes in tired soil alongside any lime/sulfur plan from the soil amendment tool

Compost is not a complete N-P-K fertilizer with a guaranteed analysis — it is soil food and structure. Hungry heavy feeders may still want a planned fertility program.

A weekend workflow that stays in band

Saturday: collect two totes of dried leaves (60) and one tote of mixed greens (kitchen scraps 15 plus a thin grass layer 17). That three-tote sketch is already closer to brown-heavy; add a fourth green tote if the calculator still reads above 30. Moisten as you layer. Sunday: turn last month’s pile into the neighboring bay so air reaches the core.

Keep a laminate card of our C:N table taped to the bin lid. When a neighbor drops a truckload of wood chips (400), do not celebrate until you have a greens plan — chips alone are a carbon mountain.

If the pile freezes solid in January, pause. Cold composting continues slowly; hot composting waits for thaw. Do not soak a frozen heap and walk away into an ice block. In summer, a hose-end spray and a turn after adding dry leaves prevents the “wet garbage core / dry leaf crust” sandwich that never mixes itself. When the finished compost looks dark and crumbly and no longer heats after turning, it is ready to screen — patience beats burying half-finished chunks around tomato stems.

Bottom line

Aim for 25–30:1. Use our C:N table — greens 15–17, leaves 60, straw 80, chips 400 — and a volumetric mix check. Expect finished compost near ⅓ of the starting volume. Fix smells with browns and air; fix stalls with greens and moisture. Let the compost calculator referee the pile before you add another mystery bucket.