Composting Carbon-to-Nitrogen Ratio Calculator

The carbon-to-nitrogen (C:N) ratio is the balance between carbon-rich "brown" materials (like cardboard and dry leaves) and nitrogen-rich "green" materials (like kitchen scraps and grass clippings) in a compost pile — getting this ratio right is what determines whether your compost breaks down efficiently or just sits there. Select your composting method and unit of measure, then choose up to three materials and enter their weights to see your blended C:N Ratio. Secondary outputs include an Assessment of how your mix compares to the ideal range, plus Total Weight, Total Carbon, and Total Nitrogen values.

Results

C:N Ratio

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Assessment

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Total Weight

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Total Carbon

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Total Nitrogen

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Frequently Asked Questions

What is the carbon-to-nitrogen ratio in composting?

The C:N ratio is the balance between carbon-rich 'brown' materials and nitrogen-rich 'green' materials in your compost. It's essential for proper decomposition and preventing odors.

What is the ideal C:N ratio for composting?

For traditional composting, aim for a C:N ratio of 25-30:1. For vermicomposting (worm bins), a slightly lower ratio of 20-25:1 works best since worms prefer less carbon-heavy mixtures.

Do I need to be exact with my C:N ratio?

No, you don't need to be perfectly precise. Getting roughly in the right range is sufficient. Your compost will still work with ratios between 20:1 and 40:1, though it may decompose slower or faster.

What happens if my C:N ratio is too high?

A high C:N ratio (too much carbon/browns) will slow down decomposition significantly. Your compost pile will take much longer to break down, but it won't smell bad or attract pests.

What happens if my C:N ratio is too low?

A low C:N ratio (too much nitrogen/greens) will cause your compost to become slimy, smelly, and anaerobic. You'll notice ammonia odors and possible pest problems.

What are examples of carbon-rich 'brown' materials?

Brown materials include dry leaves, cardboard, newspaper, sawdust, straw, and wood chips. These materials are typically dry and provide the carbon needed for composting.

What are examples of nitrogen-rich 'green' materials?

Green materials include kitchen scraps, grass clippings, coffee grounds, and fresh manure. These materials are usually moist and provide the nitrogen needed for microbial activity.

How can I adjust my compost ratio if it's not optimal?

If your ratio is too high (too much carbon), add more greens like kitchen scraps or grass clippings. If it's too low (too much nitrogen), add more browns like dry leaves or shredded paper.