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Compost Calculator

Calculate the perfect C:N ratio for your compost

Add Compost Materials

Your Compost Pile

🟤

Dry Leaves

C:N ratio 60:1

10 lbs
🟢

Grass Clippings

C:N ratio 20:1

5 lbs

Carbon to Nitrogen Ratio

46.7:1

Too Carbon-Rich

Brown Materials

10 lbs

Green Materials

5 lbs

Recommendation

Your pile is too carbon-rich (too brown). Add more green materials like grass clippings, food scraps, or coffee grounds.

C:N Ratio Guide

Below 20:1Too much nitrogen - smelly, slimy
25-30:1Ideal - fast decomposition
Above 40:1Too much carbon - slow to decompose

Green vs Brown Ratio

Green (Nitrogen-rich)5 lbs
Brown (Carbon-rich)10 lbs
C:N Ratio: 46.7:1 (ideal: 25-30:1)78%
Moisture: 40% (ideal: 40-60%)40%

Frequently Asked Questions

Q

What is the ideal C:N ratio for compost?

The ideal carbon to nitrogen (C:N) ratio is 25-30:1. This ratio allows microorganisms to decompose materials efficiently. Too much carbon (above 40:1) slows decomposition; too much nitrogen (below 20:1) causes odors and nitrogen loss.

  • Below 20:1 — Too much nitrogen, pile becomes slimy and smelly
  • 25-30:1 — Ideal range for fast, efficient decomposition
  • 30-40:1 — Acceptable but slower decomposition
  • Above 40:1 — Too much carbon, pile takes months to break down
  • Target 130-160°F internal temperature for hot composting
Q

What are the C:N ratios of common compost materials?

Brown materials are carbon-rich: dry leaves (60:1), straw (80:1), cardboard (350:1), sawdust (400:1). Green materials are nitrogen-rich: grass clippings (20:1), food scraps (15:1), coffee grounds (20:1), fresh manure (15:1).

  • Green materials provide nitrogen for microbial growth
  • Brown materials provide carbon for energy and structure
  • Higher C:N ratio = more carbon-rich material
  • Materials with C:N under 30:1 are typically "greens"
  • Materials with C:N over 30:1 are typically "browns"
MaterialC:N RatioTypeMoisture
Grass clippings20:1Green80%
Food scraps15:1Green80%
Coffee grounds20:1Green65%
Fresh manure15:1Green60%
Dry leaves60:1Brown20%
Straw80:1Brown10%
Cardboard350:1Brown5%
Sawdust400:1Brown20%
Wood chips500:1Brown15%
Q

How do I fix smelly compost?

Smelly compost usually has too much nitrogen (green materials) or is too wet. Add brown materials like dry leaves or shredded cardboard, turn the pile to add oxygen, and avoid adding more food scraps until the smell subsides.

  • Ammonia smell: Too much nitrogen — add browns (leaves, straw)
  • Rotten egg smell: Anaerobic (no oxygen) — turn the pile
  • Sour smell: Too wet — add dry browns, improve drainage
  • Turn pile every 1-2 weeks for oxygen circulation
  • Cover pile during rain to prevent waterlogging
Q

Why is my compost not decomposing?

Slow decomposition often means too much carbon, not enough moisture, or poor aeration. Add more green materials, ensure the pile is as moist as a wrung-out sponge, and turn it regularly to introduce oxygen.

ProblemLikely CauseFix
Not heating upToo much carbon (C:N > 40:1)Add grass clippings or food scraps
Smelly / slimyToo much nitrogen (C:N < 20:1)Add dry leaves, straw, or cardboard
Dry and dustyNot enough moistureWater to "wrung-out sponge" level (40-60%)
Matted / compactedNo oxygenTurn pile, add straw for air pockets
Attracting pestsExposed food scrapsBury food under 4-6" of browns
Q

How much brown to green should I add?

By volume, aim for about 2-3 parts brown to 1 part green materials. However, this varies by material density. Use this calculator to check your actual C:N ratio based on the specific materials you're adding.

  • 2:1 by volume (brown:green) is a good starting rule
  • By weight, ratio depends on material density
  • Grass clippings are heavy; leaves are light
  • Shred cardboard and straw for faster decomposition
  • Layer greens and browns like lasagna for even mixing
RecipeBrownsGreensApprox. C:N Ratio
Quick hot pile5 lbs dry leaves5 lbs grass + 3 lbs food scraps~30:1
Balanced garden8 lbs leaves + 2 lbs straw8 lbs grass + 6 lbs food scraps~29:1
Leaf-heavy fall pile15 lbs dry leaves5 lbs grass clippings~50:1 (add greens)
Kitchen scrap heavy3 lbs cardboard10 lbs food scraps~85:1 (add greens)
Q

How long does compost take to finish?

Hot composting (turned regularly, balanced C:N) finishes in 4-8 weeks. Cold composting (passive pile) takes 6-12 months. Vermicomposting (worm bin) takes 3-6 months. Smaller pieces decompose faster.

  • Hot method: 4-8 weeks with regular turning
  • Cold method: 6-12 months, minimal effort
  • Worm composting: 3-6 months for kitchen scraps
  • Chop/shred materials for faster breakdown
  • Finished compost smells earthy, is dark and crumbly

Example Calculations

1Leaf-Heavy Pile (Too Much Carbon)

Inputs

Dry Leaves10 lbs (C:N 60:1)
Grass Clippings5 lbs (C:N 20:1)

Result

C:N Ratio46.7:1
Brown Materials10 lbs
Green Materials5 lbs
Moisture Level40%
StatusToo Carbon-Rich

Total carbon = (10 × 60) + (5 × 20) = 700. Total nitrogen = 10 + 5 = 15. C:N ratio = 700 / 15 = 46.7:1. This is above 40:1, so more green materials (food scraps, grass) are needed to speed decomposition.

2Three-Material Mix (Near Ideal)

Inputs

Dry Leaves8 lbs (C:N 60:1)
Grass Clippings8 lbs (C:N 20:1)
Food Scraps6 lbs (C:N 15:1)

Result

C:N Ratio33.2:1
Brown Materials8 lbs
Green Materials14 lbs
Moisture Level55%
StatusIdeal Range

Total carbon = (8 × 60) + (8 × 20) + (6 × 15) = 480 + 160 + 90 = 730. Total nitrogen = 8 + 8 + 6 = 22. C:N ratio = 730 / 22 = 33.2:1. This falls in the 20-40:1 ideal range for efficient composting.

3Perfect Balanced Pile (Ideal C:N)

Inputs

Dry Leaves5 lbs (C:N 60:1)
Grass Clippings10 lbs (C:N 20:1)
Food Scraps8 lbs (C:N 15:1)

Result

C:N Ratio27.0:1
Brown Materials5 lbs
Green Materials18 lbs
Moisture Level63%
StatusIdeal Range

Total carbon = (5 × 60) + (10 × 20) + (8 × 15) = 300 + 200 + 120 = 620. Total nitrogen = 5 + 10 + 8 = 23. C:N ratio = 620 / 23 = 27.0:1. This is in the sweet spot of 25-30:1 for fast, efficient decomposition.

Formulas Used

Carbon-to-Nitrogen Ratio

C:N Ratio = Total Carbon / Total Nitrogen

Calculates the overall C:N ratio of the compost pile by summing the carbon and nitrogen contributions of each material.

Where:

Total Carbon= Sum of (weight × C:N ratio) for each material
Total Nitrogen= Sum of weights for all materials

Moisture Level

Moisture % = (Sum of weight × moisture%) / Total Weight × 100

Estimates the overall moisture content of the pile based on each material's moisture percentage.

Where:

weight= Weight of each material in lbs
moisture%= Moisture content percentage of each material

Green vs Brown Weight

Green Weight = Sum of weights where type = "green" | Brown Weight = Sum of weights where type = "brown"

Tracks the total weight of nitrogen-rich (green) vs carbon-rich (brown) materials in the pile.

Where:

Green= Nitrogen-rich materials: grass, food scraps, coffee grounds, manure
Brown= Carbon-rich materials: dry leaves, straw, cardboard, sawdust, wood chips

Mastering Compost Balance

Successful composting depends on achieving the right balance between carbon-rich "browns" and nitrogen-rich "greens." The ideal C:N ratio of 25-30:1 creates optimal conditions for beneficial microorganisms to break down organic matter quickly and efficiently.

Browns provide energy for microbes and add structure to the pile, while greens provide the protein microbes need to grow and reproduce. Without enough nitrogen, decomposition stalls. Without enough carbon, the pile becomes slimy, anaerobic, and smelly.

Temperature, moisture, and oxygen also matter. A well-balanced pile should heat up to 130-160°F in the center, killing weed seeds and pathogens. Turn the pile every 1-2 weeks to maintain oxygen levels and even decomposition.

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Last Updated: Feb 13, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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