EcoTrack

Compost C:N Ratio Calculator

Balance your compost pile's greens and browns.

Green material mass (kg)

Green material C:N ratio

Brown material mass (kg)

Brown material C:N ratio

Blended C:N ratio

35.451

Mass-weighted approximation — ideal compost sits around 25-30:1

What you entered

Green material mass (kg): 5Green material C:N ratio: 15Brown material mass (kg): 10Brown material C:N ratio: 100

1
Split greens into carbon and nitrogen
5 kg at 15:1= 4.6875 kg C, 0.3125 kg N
2
Split browns into carbon and nitrogen
10 kg at 100:1= 9.901 kg C, 0.099 kg N
3
Blended C:N = total C ÷ total N
14.5885 ÷ 0.4115= 35.4511:1

Result

Blended C:N ratio: 35.451

This mix has a blended C:N ratio of about 35.5:1 — on the carbon-rich side, add more greens.

Blended carbon-to-nitrogen ratio for a compost pile

A compost pile works best between about 25:1 and 30:1. The blend is total carbon divided by total nitrogen, using greens at 15:1 and browns at 60:1 unless noted.

Greens	Browns	Blended C:N	Verdict
20 kg at 15:1	10 kg at 60:1	20.22:1	Too much nitrogen, may smell
10 kg at 15:1	10 kg at 60:1	24.35:1	Slightly rich, acceptable
10 kg at 15:1	20 kg at 60:1	30.48:1	Ideal
10 kg at 15:1	30 kg at 60:1	34.82:1	Slightly slow
10 kg at 20:1	15 kg at 80:1	36.80:1	Slow, add greens
10 kg at 15:1	40 kg at 60:1	38.04:1	Too carbon-heavy, will stall

Roughly two parts browns to one part greens by mass lands in the ideal band. Note this is total carbon over total nitrogen, not an average of the two ratios: averaging overstates the blend badly, because carbon-rich browns contribute almost no nitrogen to the denominator.

The ratio that makes or breaks a compost pile

Microbes that break down compost need both carbon (energy) and nitrogen (protein-building) in roughly a 25-30:1 ratio — too much carbon (browns: dry leaves, cardboard) and decomposition slows down; too much nitrogen (greens: food scraps, grass clippings) and the pile turns slimy and smelly.

How the blend is actually calculated

The blended ratio is total carbon divided by total nitrogen, not an average of the two input ratios. That distinction matters: averaging 15:1 and 60:1 across equal masses suggests 37.5:1, when the real blend is about 24:1, because carbon-rich browns contribute almost no nitrogen to the denominator. Real compost science also weighs moisture content and particle size, but the C:N ratio is the single biggest lever for a healthy pile.

Frequently asked questions

I have 5 kg of food scraps (C:N about 15:1) and 10 kg of dry leaves (C:N about 50:1) — what is the blended ratio?

Split each material into carbon and nitrogen first: the scraps hold 4.69 kg C and 0.31 kg N, the leaves 9.80 kg C and 0.20 kg N. Blended C:N = 14.49 ÷ 0.51 = 28.5:1, which sits inside the ideal 25-30:1 band. Note that averaging the two ratios by mass instead would suggest 38.3:1 and wrongly tell you to add greens.

What is the ideal C:N ratio for composting?

Between 25:1 and 30:1. This ratio gives microbes enough carbon for energy and enough nitrogen for growth. Below 20:1 the pile tends to smell; above 40:1 decomposition slows significantly.

How does composting relate to the carbon footprint calculator?

Food waste in landfills produces methane, a greenhouse gas 28 times more potent than CO2. Composting avoids those methane emissions. The carbon footprint calculator can help quantify the emissions you prevent by diverting waste to compost.

What are examples of greens vs browns?

Greens (nitrogen-rich, C:N 10-25): food scraps, coffee grounds, fresh grass clippings. Browns (carbon-rich, C:N 30-80): dry leaves, cardboard, straw, sawdust. Mixing by mass in roughly a 2:1 browns-to-greens ratio usually hits the sweet spot.

My compost pile smells bad — is the C:N ratio wrong?

Likely too much nitrogen (too many greens). Add brown materials like shredded cardboard or dry leaves to raise the C:N ratio. Turning the pile to add oxygen also helps reduce anaerobic odor.