Compost Carbon:Nitrogen Ratio

Mix "brown" carbon-rich and "green" nitrogen-rich materials to reach the ideal 25–30 : 1 compost C:N ratio, free online.

Green material (kg)

Green C:N ratio (grass ≈ 20, food scraps ≈ 15)

Green nitrogen (% of dry weight)

Brown material (kg)

Brown C:N ratio (dry leaves ≈ 60, straw ≈ 80)

Brown nitrogen (% of dry weight)

Target C:N

About this calculator

Hot composting works best at a C:N ratio of about 25–30 : 1. Each material contributes nitrogen N = mass × %N and carbon C = N × (C:N). The combined ratio is ΣC ÷ ΣN. The tool also tells you how much brown material to add to a given amount of greens to reach your target.