Compost C:N Ratio Calculator
Calculate the weighted-average carbon-to-nitrogen ratio of a two-material compost mix. Fast, free, and fully client-side.
Calculator Inputs
How the Compost C:N Ratio Calculator Works
Calculates the weighted-average carbon-to-nitrogen (C:N) ratio of a compost pile made from two materials, using representative C:N values from the Cornell Waste Management Institute's compost materials reference table — the standard citation for these figures in composting guidance. Compares the result to the widely recommended ideal range of roughly 25:1 to 30:1 and reports whether the mix needs more "browns" (carbon-rich) or "greens" (nitrogen-rich) material.
Formula
Overall C:N = (WeightA × RatioA + WeightB × RatioB) ÷ (WeightA + WeightB)
Each material's individual C:N ratio is weighted by how much of it (by weight) goes into the mix, giving the effective C:N ratio of the combined pile.
Calculation Example
10 lbs kitchen scraps (15:1) + 20 lbs dry leaves (60:1): (10×15 + 20×60) / 30 = (150 + 1200) / 30 = 45:1.
Frequently Asked Questions
What is the ideal compost C:N ratio?
Roughly 25:1 to 30:1 is the commonly recommended range for active, efficient decomposition — too much carbon slows the pile down, too much nitrogen can turn it slimy and smelly.
Are these C:N values exact for my specific materials?
They are representative averages from published composting references. Actual ratios vary with moisture content, plant maturity, and specific material source, so treat the result as a solid planning estimate.
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