Compost Calculator

lbs
Grass, food scraps, coffee grounds — C:N ~15:1
lbs
Dry leaves, straw, cardboard — C:N ~60:1
Biology

Calculate the right balance of green and brown materials to achieve an ideal carbon-to-nitrogen (C:N) ratio for fast composting.

Formula

C:N = (greenMass × 15 + brownMass × 60) ÷ (greenMass + brownMass)
  • Ideal compost C:N ratio is 25–35:1.
  • Green materials have roughly C:N of 15:1 (grass clippings, food waste).
  • Brown materials have roughly C:N of 60:1 (dry leaves, cardboard).

10 lbs green + 30 lbs brown

Inputs
  • Green Material (nitrogen-rich): 10 lbs
  • Brown Material (carbon-rich): 30 lbs

(10×15 + 30×60) / 40 = (150+1800)/40 = 1950/40 = 48.75:1 — too carbon-rich; add more greens.

Frequently asked questions

What is the ideal C:N ratio?
25–35:1. Ratios below 25 can smell; above 35 decompose slowly.
What counts as green?
Grass clippings, fruit/veggie scraps, coffee grounds, fresh leaves.