Compost Ratio Calculator

Successful composting depends on the right balance of carbon-rich “brown” materials and nitrogen-rich “green” materials.

The ideal carbon-to-nitrogen (C:N) ratio is approximately 25:1 to 30:1. This ratio provides the optimal environment for decomposition microorganisms.

Why the ratio matters:

• Too much carbon (too many browns): Decomposition slows dramatically. The pile may sit for months with little change.
• Too much nitrogen (too many greens): The pile becomes slimy, compacted, and smelly (ammonia odor).
• Just right: The pile heats up quickly, breaks down efficiently, and produces rich, dark compost.

Common brown materials (carbon-rich):

• Dry leaves: C:N ratio ~60:1
• Straw: C:N ratio ~75:1
• Cardboard: C:N ratio ~350:1
• Wood chips: C:N ratio ~400:1
• Newspaper: C:N ratio ~175:1
• Sawdust: C:N ratio ~325:1

Common green materials (nitrogen-rich):

• Grass clippings: C:N ratio ~17:1
• Kitchen scraps (fruit/veg): C:N ratio ~15:1
• Coffee grounds: C:N ratio ~20:1
• Fresh garden waste: C:N ratio ~25:1
• Manure (herbivore): C:N ratio ~15:1

Volume rule of thumb: Since browns are much higher in carbon per unit than greens are in nitrogen, the volume ratio works out to roughly 3 parts brown to 1 part green by volume for most common materials.

Additional requirements:

• Moisture: The pile should feel like a wrung-out sponge.
• Air: Turn the pile every 1-2 weeks to introduce oxygen.
• Size: Minimum 3×3×3 feet (1×1×1 m) to generate enough heat.