Compost C:N Ratio Calculator

Getting the microbial diet right

Compost microorganisms work most efficiently within a specific carbon-to-nitrogen ratio range - blending carbon-rich "brown" materials (dry leaves, straw, cardboard) with nitrogen-rich "green" materials (grass clippings, food scraps) in the right proportion is central to successful composting.

Worked example

For 3 volume units of carbon material (C:N 60:1) blended with 1 volume unit of nitrogen material (C:N 15:1):

Blended C:N = ((3 x 60) + (1 x 15)) / 4 = 48.75:1 (Too carbon-rich - add more nitrogen (greens) to speed decomposition)

Frequently asked questions

What happens with too much nitrogen? Excess nitrogen relative to carbon creates smelly, anaerobic conditions as microbes struggle to process the excess - this is the common cause of a foul-smelling compost pile.

What happens with too much carbon? Excess carbon relative to nitrogen dramatically slows decomposition, since microbes lack enough nitrogen to build new cells efficiently - a pile that seems to never break down is often simply too carbon-heavy and needs more nitrogen-rich material mixed in.