Compost Carbon-to-Nitrogen Ratio Calculator
Add your compost ingredients by weight to get the blended carbon-to-nitrogen ratio. See whether to add more browns or greens to reach the ideal 25-35:1 ratio. Nothing uploaded.
Add Ingredients
Pile C:N Ratio
Add materials to see your C:N ratio.
Learn more: compost C:N ratios and pile balance
Why the C:N ratio matters
The ideal carbon-to-nitrogen ratio for active hot composting is 25:1 to 35:1. Below 20:1 means too much nitrogen, and the pile gets smelly and anaerobic. Above 40:1 means too much carbon, and decomposition slows dramatically. The "two-thirds browns, one-third greens" rule is a useful starting point, but actual C:N ratios vary enormously - dry leaves have a C:N of 50:1 while fresh grass is 17:1.
Browns vs greens: the material divide
Browns are carbon-rich materials: cardboard, dry leaves, straw, wood chips, and sawdust. Greens are nitrogen-rich materials: fresh grass clippings, food scraps, coffee grounds, and manure. A healthy pile needs both. The calculator lets you build your pile from actual materials and weights, showing the blended C:N ratio and whether you need more browns or greens to reach the ideal 25-35:1 range.
Fixing an unbalanced pile
If your pile smells bad or attracts flies, it likely has too much nitrogen (C:N below 20:1). Add dry cardboard, straw, dry leaves, or wood chips to bring the ratio up. Also ensure adequate aeration by turning the pile regularly. If decomposition is slow, you may have too much carbon - add fresh grass or food scraps to speed it up.
FAQ
What is the ideal C:N ratio for compost?
25:1 to 35:1 for active hot composting. Below 20:1: too much nitrogen, pile gets smelly. Above 40:1: too much carbon, slow decomposition.
What are browns and greens in composting?
Browns are carbon-rich: cardboard, dry leaves, straw, wood chips. Greens are nitrogen-rich: fresh grass, food scraps, coffee grounds, manure. Both needed for a balanced pile.
Why does my compost smell bad?
Too much nitrogen (C:N below 20:1). Add dry cardboard, straw, or leaves to bring the ratio up. Also ensure adequate aeration by turning regularly.