Compost C:N Ratio Calculator

Use this compost calculator to check the carbon-to-nitrogen ratio of your compost pile.

Enter your brown materials (carbon-rich) and green materials (nitrogen-rich) weights to get the ideal mix for fast decomposition.

Browns (Carbon-rich)

Dry leaves, straw, sawdust, newspaper, cardboard

Brown material weight (lbs)

Greens (Nitrogen-rich)

Food scraps, coffee grounds, grass clippings, manure

Green material weight (lbs)

Results

Current C:N ratio

38.3:1

Ideal range: 25:1 to 30:1

Recommendation

Too carbon-rich. Add more green materials (food scraps, coffee grounds, grass clippings).

💡 Add ~8.3 lbs of green material to reach 30:1

Detailed Explanation

🎯 Purpose

This compost C:N ratio calculator helps you check if your compost pile has the ideal carbon-to-nitrogen ratio (25:1 to 30:1). The right balance helps compost decompose faster.

📝 How to Use

1. Enter the weight of brown materials (carbon-rich): dry leaves, straw, sawdust, newspaper, cardboard. 2. Enter the weight of green materials (nitrogen-rich): food scraps, coffee grounds, grass clippings, manure. 3. The calculator will show your current C:N ratio. 4. If it's too high (too much carbon), add more greens. If too low (too much nitrogen), add more browns.

🔢 Algorithm

Brown materials average C:N = 50:1 Green materials average C:N = 15:1 Weighted average C:N = (Brown weight × 50 + Green weight × 15) ÷ (Brown weight + Green weight) Ideal range: 25:1 to 30:1 - Above 30:1 → too carbon-rich, add green materials - Below 25:1 → too nitrogen-rich, add brown materials

💡 Why do it this way?

Why is the ideal C:N ratio 25:1 to 30:1? Microbes in your compost pile (bacteria and fungi) need carbon for energy and nitrogen to build their bodies. Think of it like our diet: carbon is rice (energy), nitrogen is meat (building material). - Too much carbon (>30:1): Microbes are "full of carbs" but don't have enough protein to multiply fast — decomposition slows down and the pile may take 6 months to finish. - Too much nitrogen (<25:1): Microbes eat "too much meat" and produce ammonia (that rotten egg smell), which volatilizes and wastes fertilizer. - 25-30:1 is the microbes' "golden ratio" — they're well-fed and multiply fast, so compost finishes in 4-6 weeks. 📚 Sources: • Cornell Composting Research Center: https://compost.css.cornell.edu/chemistry.html • USDA Compost Guide: https://www.ams.usda.gov/sites/default/files/media/Compost_FINAL.pdf • Utah State University Extension: https://extension.usu.edu/agwastemanagement/files/Compost_Fundamentals.pdf