Compost C:N Ratio Calculator
By Santaji GadepatilinUpdated October 27, 2026
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How to use this calculator
Enter the weight, carbon % and nitrogen % of a brown and a green material. The C:N ratio of the mix is calculated. Adjust the weights until you reach about 25–30.
Formula
C:N = (m₁C₁ + m₂C₂) ÷ (m₁N₁ + m₂N₂)
Example
10 kg leaves (50% C, 0.8% N) + 15 kg food scraps (40% C, 2.5% N):
C:N = (5 + 6) ÷ (0.08 + 0.375) = 24.2 : 1
Frequently asked questions
What is the ideal C:N ratio for compost?
About 25–30 : 1. Too much carbon composts slowly; too much nitrogen can smell of ammonia.
What are greens and browns?
Greens (food scraps, grass) are nitrogen-rich; browns (dry leaves, straw, cardboard) are carbon-rich.
Where do I find carbon and nitrogen content?
Use published tables for common materials. Dry leaves are often 40–80 : 1, food scraps about 15 : 1.