Compost Ratio Calculator

About this calculator

Composting works best with a carbon-to-nitrogen (C:N) ratio around 25–30:1 by mass, but since gardeners measure ingredients by the bucket or barrow rather than by weight, this calculator uses the practical rule of thumb of mixing browns and greens by volume instead — commonly 2 or 3 parts browns (dry, carbon-rich material like dead leaves, straw, or cardboard) to 1 part greens (moist, nitrogen-rich material like grass clippings, vegetable scraps, or coffee grounds), since browns are typically less dense than greens.

Home composters and market gardeners use this volume ratio to keep a pile from turning slimy and anaerobic (too many greens, not enough air) or from stalling out and failing to heat up (too many browns, not enough nitrogen for the microbes). Getting the mix roughly right speeds up decomposition and helps the pile reach the internal temperatures needed to break down material efficiently and suppress weed seeds and pathogens.