Compost Calculator

Fast, efficient decomposition in a compost pile comes down to the balance between carbon (C) and nitrogen (N). Hold that ratio in the sweet spot, ideally between 25:1 and 30:1, and your organic matter breaks down quickly into the nutrient-rich compost that healthy gardens and sustainable farming depend on.

To estimate your pile's overall C:N ratio, this tool divides total carbon by total nitrogen, the formula the Cornell Waste Management Institute uses, with two material classes: greens, counted at 20:1, and browns, counted at 60:1. It assumes both classes carry the same share of carbon per pound, so each pound of greens brings 1/20 of that as nitrogen and each pound of browns 1/60, and the mix ratio is the total weight divided by the total nitrogen. Above 30:1 it tells you how many pounds of greens bring the mix to 27.5:1; below 25:1, how many pounds of browns. Treat the result as a rough guide: real materials differ in carbon content, C:N and moisture, which Cornell's full calculation takes into account.

Misjudging the inputs is the usual stumbling block, whether that means lowballing the C:N ratio of 'greens' or overstating the 'browns', so lean on a reliable C:N chart for each material. Diseased plants and pet waste are worth keeping out entirely, since they can carry pathogens or breed foul odors. Frequent turning matters too: aerating the pile fuels the microbial activity that drives decomposition no matter where the C:N ratio lands.