Composting

Compost Ratio Calculator

Add your greens and browns to see your pile's weighted carbon-to-nitrogen ratio on a gauge, or use the simple volume-ratio mode if you'd rather not weigh anything.

—Estimated pile C:N ratio
10:1Ideal ~25–30:160:1

Calculated on your device. Nothing is uploaded to a server.

Why the green-brown balance matters

Too many nitrogen-rich greens and a pile turns slimy and smelly; too many carbon-rich browns and it barely breaks down at all. Getting the ratio roughly right speeds everything up.

Faster breakdown

A balanced C:N ratio keeps the microbes that do the actual composting working efficiently.

Less smell, less mess

Too much nitrogen without enough carbon is the usual cause of a soggy, odorous pile.

Two ways to plan

Weigh materials for a precise estimate, or use the simple volume rule of thumb if that's easier.

How to use the calculator

  1. Pick a modeUse C:N by material for a weighted estimate, or Simple volume ratio for a quick rule-of-thumb split.
  2. Add your materialsChoose each green or brown you're using and enter an amount.
  3. Read the gaugeSee whether your mix is below, within or above the ideal C:N range.
  4. Adjust as suggestedAdd more of whichever material the note recommends and watch the ratio update.

Understanding the carbon-to-nitrogen ratio

Compost microbes need both carbon, mostly for energy, and nitrogen, mostly for building their own cells, and they use them in a fairly consistent proportion. A widely cited general guideline puts the ideal starting mix at roughly 25:1 to 30:1 carbon to nitrogen by weight — noticeably more carbon than nitrogen, since a lot of the carbon is used up as energy rather than incorporated into new microbial growth. In everyday composting terms, "greens" like grass clippings, food scraps, coffee grounds and fresh manure tend to be nitrogen-rich with a low C:N ratio, often well under 20:1, while "browns" like dry leaves, straw, cardboard, wood chips and sawdust are carbon-rich with a high C:N ratio, sometimes well over 100:1. Because a handful of straw and a handful of grass clippings weigh very differently, this calculator computes a weighted average based on the amount of each material you enter rather than simply averaging the ratios, which gives a much more realistic estimate of the whole pile.

~8 built-in materials

Common greens and browns each with an approximate C:N ratio.

Weighted, not averaged

Larger amounts of a material count for more, just like in a real pile.

Volume mode included

A simpler rule-of-thumb option when weighing materials isn't practical.

Compost ratio FAQ

What is a carbon-to-nitrogen (C:N) ratio?

It's the proportion of carbon-rich material to nitrogen-rich material in a compost pile, usually written like 30:1. Microbes that break down compost need both elements in roughly this balance to work efficiently without the pile turning slimy or smelly, or staying inert and dry.

What's a good target C:N ratio for compost?

A commonly cited general guideline is roughly 25:1 to 30:1 by weight. This calculator treats that range as the ideal zone on the gauge, though real piles work across a fairly wide range around it.

How is the weighted ratio calculated?

Each material you add contributes its own approximate C:N ratio in proportion to the amount you entered. The calculator averages these contributions weighted by amount to estimate the overall ratio of the whole pile.

What does the volume-ratio mode do?

It's a simpler fallback for anyone who doesn't want to weigh individual materials. Enter a total pile volume and a green-to-brown ratio target (a commonly cited rule of thumb is roughly 1 part greens to 2 or 3 parts browns by volume), and it suggests how much of each to use.

Are these C:N values exact?

No. They're approximate figures widely cited in composting guides. Actual carbon and nitrogen content varies with moisture, freshness and exact material, so use the result as a starting point and adjust based on how your pile looks, feels and smells.

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