Compost Calculator

About This Tool

The Compost Calculator serves two purposes: calculating your compost bin volume and optimizing the carbon-to-nitrogen ratio of your material mix. Getting the C:N ratio right is the single most important factor in producing compost quickly and without odor problems.

The Carbon-to-Nitrogen Ratio

Composting microorganisms need both carbon (for energy) and nitrogen (for protein). The ideal ratio is 25:1 to 35:1 carbon to nitrogen. Too much nitrogen (below 25:1) creates a smelly, slimy mess. Too much carbon (above 35:1) slows decomposition to a crawl. The classic shorthand is 3 parts brown to 1 part green by volume, though exact ratios vary by material.

Green vs Brown Materials

Green materials are nitrogen-rich: grass clippings, food scraps, coffee grounds, fresh manure, and green plant trimmings. Brown materials are carbon-rich: dry leaves, straw, cardboard, wood chips, and newspaper. Despite the name, some "greens" aren't actually green (coffee grounds, manure) and some "browns" can be colorful (fall leaves). The classification is about nutrient content, not color.

Bin Size Recommendations

The minimum effective compost bin size is about 3x3x3 feet (27 cubic feet). Smaller piles don't retain enough heat for efficient decomposition. A 4x4x3 bin is ideal for most households. Very large piles (over 5x5x5) can become anaerobic in the center without frequent turning. Two or three bins allow you to have compost at different stages simultaneously.

Speeding Up Decomposition

Shred or chop materials into smaller pieces to increase surface area. Maintain moisture like a wrung-out sponge. Turn the pile every 1-2 weeks to introduce oxygen. Getting the C:N ratio right from the start prevents most composting problems. A well-managed hot compost pile can produce finished compost in 4-8 weeks. A passive pile takes 6-12 months.