🍂 Compost Carbon-to-Nitrogen (C:N) Ratio Calculator
Blend your ‘browns’ and ‘greens’ in the right proportions by calculating the combined carbon-to-nitrogen ratio of your compost pile, targeting the ideal range of around 25:1 to 30:1.
Why the carbon-to-nitrogen ratio matters
Compost microbes need both carbon (energy) and nitrogen (protein-building blocks) in the right proportion to break down material efficiently without going anaerobic or losing excess nitrogen as ammonia. The widely recommended target for active composting is a carbon-to-nitrogen (C:N) ratio of roughly 25:1 to 30:1 by dry weight. ‘Brown’ materials (dry leaves, straw, cardboard) are carbon-rich, while ‘green’ materials (grass clippings, food scraps, fresh garden waste) are nitrogen-rich.
How this calculator works
Enter the wet weight, approximate moisture content, and known C:N ratio for your brown material and your green material. The calculator first converts each wet weight to a dry weight (since C:N ratios are defined on a dry-matter basis), then combines them using the standard weighted-blend formula for two feedstocks with similar carbon content: Blended C:N = Total Dry Weight ÷ (Dry Weight 1 ÷ C:N 1 + Dry Weight 2 ÷ C:N 2).
Typical reference C:N ratios: dry leaves ~60:1, straw ~75:1, wood chips ~400:1, grass clippings ~15-20:1, vegetable scraps ~15:1, coffee grounds ~20:1. This calculator is for general composting guidance and educational planning; actual decomposition also depends on particle size, aeration, and moisture management.