Compost Carbon-to-Nitrogen (C:N) Ratio Calculator
Enter the weight and carbon/nitrogen content of multiple compost ingredients to compute the blended C:N ratio and check the ideal 25:1 β 30:1 range.
Compost Material Mix
Enter the weight (kg) of each ingredient plus its carbon (C) and nitrogen (N) percentages. The tool computes the blended C:N ratio. The ideal compost C:N ratio is about 25:1 β 30:1.
| Material | Weight (kg) | Carbon C % | Nitrogen N % |
|---|
Common Compost Materials
Click a preset pill above to fill typical C/N data, or edit any value. Figures are standard approximate (wet-basis) references.
| Material | Carbon C % | Nitrogen N % | Approx C:N | Type |
|---|
Formula
Blended C:N = total carbon mass Γ· total nitrogen mass, where:
Total C = Ξ£( weight_i Γ C_i% / 100 )
Total N = Ξ£( weight_i Γ N_i% / 100 )
Blended C:N = Total C Γ· Total N
Because C:N is a ratio, the weight unit (kg or lb) does not affect the result β it only changes the displayed total mass.
Frequently Asked Questions
What is the carbon-to-nitrogen ratio (C:N)?
The C:N ratio is the mass ratio of carbon to nitrogen in compost feedstock. Carbon fuels microbial energy ("browns"), while nitrogen builds microbial protein ("greens"). Too high slows decomposition; too low causes ammonia odor and nitrogen loss.
Why is 25:1 β 30:1 the ideal range?
Research and practice show that a C:N between 25 and 30 gives the highest microbial activity, fastest curing, and best nitrogen retention. A common mistake is adding too many browns (leaves, cardboard), pushing the ratio too high.
My ratio is too high (carbon-heavy) β what do I do?
Add more "greens": kitchen scraps, grass clippings, coffee grounds, or manure, which are nitrogen-rich. A small amount of urea (~46% N) can also rebalance the mix.
What if the ratio is too low (nitrogen-heavy)?
Excess nitrogen releases smelly ammonia and attracts pests while losing nitrogen. Add browns β dry leaves, straw, wood chips, or shredded cardboard β to raise the ratio.