Compost Calculator

The Compost Calculator blends multiple ingredients to compute the carbon-to-nitrogen (C:N) ratio, estimates composting time for 4 methods, and predicts finished volume after shrinkage. Interactive SVG ratio visualization and dynamic ingredient list — features an AI chatbot cannot replicate. Free, no sign-up required.

Composting Method

Ingredients

1Green (nitrogen)

cu ft

Results

C:N Ratio

20:1

Slightly nitrogen-rich. Consider adding a bit more brown material.

Raw Volume

1 cu ft

Finished Volume

0.4 cu ft

shrinkage

60%

Green %

100%

Brown %

Estimated Time

8 weeks

Total Weight

25 lbs

Raw Volume (cu yd)

0.04 cu yd

C:N Ratio Chart

Green/Brown Composition

Ingredient Reference

Ingredient	Category	C:N Ratio	Moisture %
Grass Clippings	Green (nitrogen)	20:1	80%
Food Scraps	Green (nitrogen)	15:1	85%
Coffee Grounds	Green (nitrogen)	20:1	60%
Chicken Manure	Green (nitrogen)	8:1	70%
Horse Manure	Green (nitrogen)	30:1	60%
Fresh Weeds	Green (nitrogen)	25:1	75%
Seaweed	Green (nitrogen)	19:1	80%
Dry Leaves	Brown (carbon)	60:1	30%
Straw	Brown (carbon)	80:1	10%
Cardboard	Brown (carbon)	350:1	5%
Newspaper	Brown (carbon)	175:1	5%
Wood Chips	Brown (carbon)	400:1	20%
Sawdust	Brown (carbon)	325:1	15%
Pine Needles	Brown (carbon)	80:1	20%
Corn Stalks	Brown (carbon)	75:1	15%

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What is a Compost Calculator?

A compost calculator helps you build the ideal compost pile by calculating the blended carbon-to-nitrogen (C:N) ratio from your available ingredients. The ideal C:N ratio for composting is between 25:1 and 35:1. Too much nitrogen (green materials) causes odor and ammonia loss; too much carbon (brown materials) slows decomposition. This calculator also estimates composting time based on your method and predicts the finished volume after shrinkage.

How to Use This Calculator

Select your composting method: hot bin, cold pile, tumbler, or vermicompost
Add ingredients from the dropdown — choose both green (nitrogen-rich) and brown (carbon-rich) materials
Enter the volume for each ingredient in cubic feet or liters
Review the blended C:N ratio — aim for 25:1 to 35:1
Check the estimated composting time and finished volume
Adjust ingredients to balance the green/brown ratio if needed

Frequently Asked Questions

What is the ideal C:N ratio for composting?

The ideal C:N ratio is between 25:1 and 35:1. At this range, microorganisms have enough nitrogen for growth and enough carbon for energy. A ratio of 30:1 is considered optimal. Below 20:1, the pile may smell of ammonia. Above 50:1, decomposition slows dramatically.

What are examples of green and brown compost materials?

Green (nitrogen-rich) materials include grass clippings (C:N 20:1), food scraps (15:1), coffee grounds (20:1), and fresh weeds (25:1). Brown (carbon-rich) materials include dry leaves (60:1), straw (80:1), cardboard (350:1), and wood chips (400:1).

How long does composting take?

Composting time depends on the method: hot composting takes 6–10 weeks, tumbler composting 4–8 weeks, vermicomposting 8–16 weeks, and cold pile composting 4–8 months. Factors like C:N ratio, moisture, aeration, and temperature all affect speed.

How much does compost shrink during decomposition?

Compost typically shrinks 50–60% during decomposition. A pile that starts at 1 cubic yard will produce about 0.4–0.5 cubic yards of finished compost. Hot composting has the highest shrinkage (up to 60%) because of faster decomposition.