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Free compost ratio calculator for carbon-to-nitrogen planning. Combine ingredients by mass to see blended C:N, or solve how many parts green vs brown hit your target ratio.
Last updated: April 8, 2026
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Blended C:N
36.6 : 1
Total dry mass
100.0 lb
Moderate—may slow slightly
In a common target band for many backyard piles (roughly ~25–30:1 is often cited).
Enter characteristic C:N for a greener (lower) and browner (higher) feedstock. The tool solves how many parts green vs brown by mass hit your target C:N.
Mass ratio (green : brown)
0.82 : 1
Green = lower C:N feedstock; brown = higher C:N. Ratio is lb green per 1 lb brown.
Model assumes each ingredient’s mass splits into carbon and nitrogen as C = (cn/(cn+1))·M and N = (1/(cn+1))·M. Use book values for your feedstocks.
Output
Blended C:N
Add rows for grass, leaves, coffee grounds, kitchen scraps, and more.
Rule of thumb
Greens lower, browns higher
Assign book values from your extension or compost reference.
Output
Mass ratio
Target must be strictly between the two C:N ratios you enter.
Field craft
Turn & dampen
Ratios help, but texture and water drive real piles.
Lab tests
Best for precision
Commercial composters use analysis; home piles use rules of thumb.
Next step
Garden fertilizer calc
After curing, use soil tests to guide feeding.
25 lb grass (20:1) + 75 lb leaves (50:1); solver 20 / 50 green-brown → target 30:1
Blended C:N
36.6 : 1
Green : brown (solver)
0.82 : 1
Carbon-to-nitrogen ratio describes how much carbon-rich versus nitrogen-rich material is in your pile. This tool uses a standard mass-balance shortcut: each ingredient’s carbon and nitrogen are inferred from its C:N so that you can mix multiple ingredients and see the combined ratio.
Blended C:N = (Σ Mᵢ · Cᵢ) / (Σ Nᵢ)with Cᵢ = (Rᵢ/(Rᵢ+1))·Mᵢ and Nᵢ = (1/(Rᵢ+1))·MᵢHere Rᵢ is the label C:N for ingredient i and Mᵢ is its dry mass in the mix.
That range is often taught as a workable balance for microbial activity and odor control in backyard systems. Cold piles, high moisture, or fine texture may behave differently—observe and adjust.
Feeding the garden? Garden fertilizer calculator and raised bed soil calculator.
Get a Custom Calculator for Your SiteThe target must sit between 20 and 50. The calculator returns how many pounds of green per pound of brown (or guidance if your green/brown fields are swapped).
Compare this ratio to what you can actually source—round to practical bucket loads.
Share it with others building a compost system
Suggested hashtags: #Compost #Gardening #Sustainability #Soil #Calculator