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Compost Ratio Calculator

Balance your compost by splitting the bin volume into the right ratio of browns and greens.

Result

150 L
50 L

How it is calculated

You give the total volume of the bin in litres and the ratio as parts of browns to parts of greens. The tool adds the parts, sum = browns + greens, then splits the volume: browns volume = total × browns / sum and greens volume = total × greens / sum. Results are rounded to whole litres, so the two figures can differ from the total by a litre.

The total must be greater than zero. If you leave the browns or greens parts empty or enter zero or less, the tool uses its default of 2 parts browns to 1 part greens. The split is by volume, not by weight, and it does not measure the actual carbon-to-nitrogen ratio of your materials, which varies with what you add and how wet it is.

Worked example

You are filling a 200 L bin and want 3 parts browns to 1 part greens. The parts add up to 3 + 1 = 4. Browns: 200 × 3 / 4 = 150 L. Greens: 200 × 1 / 4 = 50 L. Together they make the full 200 L. With the default 2:1 ratio the same bin would take 133 L of browns and 67 L of greens.

Try this example →

Common mistakes

  • Entering the volume of the greens or browns in the total field; the total is the whole bin, and the tool splits it for you.
  • Typing a ratio like 3:1 into one field; browns and greens are separate fields, here 3 and 1.
  • Swapping the two fields, which would give you three times more greens than browns and a wet, smelly pile.
  • Measuring by weight when the tool works in litres; wet greens are much denser than dry leaves, so weigh nothing and use buckets of equal size.
  • Not noticing the defaults: leaving the ratio fields blank silently gives 2:1, which may not be the ratio your materials need.

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.

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