Compost C:N Ratio Calculator
A hot, fast pile runs near a 25:1–30:1 carbon-to-nitrogen ratio. Enter the weights of your greens and browns to see your mix and what to add.
Enter the weight (lb or any consistent unit) of each material in your pile.
Add the wet/lb weights of your greens and browns to see your mix C:N.
C:N values are typical literature ratios (Cornell WMA; USDA/NRCS). Real material ratios shift with moisture and maturity, so use this as a guide, not a lab result.
C:N source: Approximate carbon-to-nitrogen ratios from composting literature (Cornell Waste Management Institute; USDA/NRCS). Material C:N varies with maturity, moisture, and source — treat as typical.
Related: Carbon footprint calculator → · Compost hub →
Frequently asked questions
What is a good C:N ratio for compost?
Most references put the sweet spot at 25:1 to 30:1 (carbon to nitrogen). Below that, the pile gets smelly and nitrogen-leachy; above it, decomposition slows because microbes lack nitrogen to build protein.
My pile is too nitrogen-rich — what do I add?
Add high-carbon browns: dry leaves (~60:1), straw (~80:1), shredded paper (~200:1), cardboard (~350:1), or wood chips (~400:1). These pull the blended ratio up toward the ideal range.
My pile is too carbon-heavy — what do I add?
Add high-nitrogen greens: vegetable scraps (~15:1), fresh grass or coffee grounds (~20:1), or manure (~20:1). A little green material goes a long way because the ratios are so different.