Free compost C:N ratio calculator. Balance brown and green materials to achieve the ideal 25-30:1 carbon-to-nitrogen ratio for fast, efficient composting.
You might also find these calculators useful
Calculate how much compost you need for gardens and beds
Calculate nitrogen, phosphorus, and potassium from any fertilizer blend
Calculate fertilizer rates based on NPK requirements
Calculate soil organic carbon stock and sequestration potential
The carbon-to-nitrogen (C:N) ratio is the key to successful composting. Microorganisms need the right balance of carbon for energy and nitrogen for protein production. Our calculator helps you mix brown and green materials to achieve the ideal 25-30:1 ratio for fast decomposition without odors.
The C:N ratio is the weight of carbon relative to nitrogen in your pile. Composting microbes work best when a fresh pile starts at about 25–30:1 (Cornell Waste Management Institute; university-extension guidance). "Browns" — dry leaves, cardboard, straw, sawdust — are carbon-rich with high ratios (60:1 to 400:1); "greens" — grass clippings, food scraps, coffee grounds, manure — are nitrogen-rich with low ratios (10:1 to 25:1). Mixing them to land in the 25–30:1 window gives fast, odor-free decomposition. This calculator weighs each material on a dry-matter basis, so wetter greens contribute less mass than their fresh weight suggests.
C:N Ratio Formula
Balance nitrogen-rich food waste with dry autumn leaves for backyard composting.
Mix fresh lawn clippings with shredded cardboard to prevent matting and odors.
Add carbon sources to nitrogen-rich animal manures for proper decomposition.
Calculate ratios for municipal or farm composting operations handling diverse materials.
The ideal 25-30:1 ratio provides optimal conditions for microorganisms to break down materials quickly.
Too much nitrogen (low ratio) causes ammonia smells. Proper balance produces earthy-smelling compost.
Balanced compost creates nutrient-rich humus perfect for gardens and plants.
The ideal range is 25:1 to 30:1. This provides enough carbon for energy and nitrogen for microbial protein synthesis. Ratios above 30:1 decompose slowly; below 25:1 may produce ammonia odors.
Browns are carbon-rich dry materials like leaves, cardboard, straw, and sawdust. Greens are nitrogen-rich materials like grass clippings, food scraps, coffee grounds, and fresh manure. The terms refer to nutrient content, not actual color.
Bad odors usually indicate too much nitrogen (low C:N ratio) or lack of oxygen. Add more brown materials and turn the pile to introduce air. A properly balanced, aerated pile should smell earthy.
Compost should be moist like a wrung-out sponge (40-60% moisture). Our calculator accounts for the moisture content of different materials to give accurate dry-weight calculations for the C:N ratio.