Compost Calculator (C:N Ratio)

The Compost Calculator (C:N Ratio) estimates the carbon-to-nitrogen balance of a compost recipe from the brown and green materials you plan to add. Enter material amounts as bucketfuls, parts, or weight-equivalent portions, then compare the result with the 25:1 to 30:1 range often used for active, low-odor composting.

Compost C:N Ratio Formula

Each ingredient has an approximate carbon-to-nitrogen ratio. The calculator converts each material amount into carbon units and nitrogen units, adds them across the recipe, and divides total carbon by total nitrogen.

For a material with a 60:1 C:N ratio, the calculator treats the material as 60 parts carbon for every 1 part nitrogen. When volume mode is selected, common bulk-density factors are applied so a bucket of fluffy dry leaves does not count like a bucket of dense food scraps.

How to Use the Compost Calculator

1. Choose the measurement mode: Use volume mode for bucketfuls or weight-equivalent mode when each amount represents the same mass.
2. Enter brown and green materials: Select each compost material and enter how many parts, buckets, or weight-equivalent portions you plan to add.
3. Add custom materials if needed: Choose Custom material and enter its C:N ratio when your ingredient is not in the list.
4. Review the balance: Click Calculate Compost Ratio to see the overall C:N ratio, layer diagram, and correction advice.

Common Compost Material C:N Ratios

Reading the Result

A result below about 20:1 usually means the mix is nitrogen-rich and may become wet or smelly. A result above about 40:1 usually means the mix is carbon-rich and may compost slowly. The ideal band is a starting point, not a guarantee: moisture, oxygen, particle size, and pile size still matter.

Practical Compost Balancing Tips

• Add browns when the pile smells sour, looks slimy, or feels too wet.
• Add greens when the pile is dry, cool, and not breaking down after mixing and watering.
• Chop coarse browns and mix wet greens into the pile instead of leaving them in one layer.
• Keep moisture near the feel of a wrung-out sponge and turn the pile when it compacts.

Frequently Asked Questions

What is the ideal C:N ratio for compost?

A starting compost mix around 25:1 to 30:1 is commonly used for active, low-odor decomposition. Slightly outside that range can still compost, but very green mixes can smell and very brown mixes can slow down.

Are browns carbon and greens nitrogen?

Browns are usually carbon-rich dry materials such as leaves, straw, paper, cardboard, sawdust, and wood chips. Greens are usually wetter nitrogen-rich materials such as grass clippings, food scraps, coffee grounds, manure, and fresh plant trimmings.

Should I measure compost ingredients by volume or weight?

Weight is more precise, but gardeners often build piles by volume. This calculator offers a volume mode that adjusts common bucketfuls with rough bulk-density factors, plus a weight-equivalent mode for weighed ingredients.

Why does a pile smell bad?

A smelly compost pile is often too wet, too compact, or too nitrogen-rich. Add dry browns, mix the pile for airflow, and keep moisture near the feel of a wrung-out sponge.

Are C:N ratios exact?

No. Compost material ratios vary with species, age, moisture, particle size, and storage. The calculator gives a planning estimate, then the pile should be adjusted by smell, moisture, heat, and texture.