Compost Ratio Calculator
"Two parts brown to one part green" can be badly wrong — cardboard is 350:1 and grass is 20:1. Pick what you actually have and get the real ratio.
C:N figures are typical published values and vary with moisture and age. Volumes are treated as equal-weight buckets — good enough for practical pile building, not laboratory work.
Frequently asked questions
What is the ideal compost ratio?
A carbon-to-nitrogen ratio between 25:1 and 30:1 by weight. Below about 20:1 the pile goes anaerobic and smells of ammonia; above about 40:1 it simply sits there and does very little. The common advice of "two parts brown to one part green" is a rough volume shortcut for this.
Why do people say browns and greens instead of carbon and nitrogen?
Because it is easier to remember. Browns are dry and carbon-rich (leaves, straw, cardboard, wood chips); greens are wet and nitrogen-rich (grass, food scraps, coffee grounds, manure). But the actual ratios vary enormously — cardboard is 350:1 while grass is 20:1, so "two to one" can be badly wrong depending on which brown you use.
My pile smells like ammonia. What do I do?
Too much nitrogen — the ratio is too low. Add carbon: dry leaves, shredded cardboard, straw. Turn it while you add so the material mixes rather than layering.
My pile is not heating up. Why?
Usually too much carbon, too little moisture, or too small a pile. Check the ratio here first; if it is above 40:1 add greens. A pile also needs to be roughly a cubic yard to hold heat, and as damp as a wrung-out sponge.
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