Compost Calculator

Balance a compost pile's carbon to nitrogen ratio and estimate yield.

About Compost Calculator

Composting works best around a 30 to 1 carbon to nitrogen ratio. Too much nitrogen produces ammonia odour while too much carbon stalls decomposition, and roughly two thirds of the mass is lost as water and carbon dioxide. Diverting food waste from landfill avoids methane emissions, which matters more than the compost produced since landfill decomposition is anaerobic.

Formula

Compost

Blended ratio = total carbon ÷ total nitrogen; the target is about 30 to 1

greens: Nitrogen-rich material such as food scraps and grass clippings
browns: Carbon-rich material such as dry leaves, cardboard and straw

Worked example

With the default values below, Compost Calculator returns Blended Carbon to Nitrogen Ratio of 43.13. Change any input above and every figure here is recalculated in your browser.

Inputs used

Nitrogen-rich green wasteminimum 0 kg: 12 kg
Carbon-rich brown wasteminimum 0 kg: 20 kg
Carbon to nitrogen ratio of greensminimum 1: 15
Carbon to nitrogen ratio of brownsminimum 1: 60
Turning intervalminimum 1 days: 7 days

Results

Blended Carbon to Nitrogen Ratio: 43.13
Expected Compost Yield: 11.20 kg
Estimated Maturation Time: 8.0 weeks
Brown Material to Add for a 30:1 Ratio: 0.00 kg
Balance Verdict: Too much carbon — decomposition will be very slow, add greens

Step by step

1Values used
2Compost
3Blended Carbon to Nitrogen Ratio= 43.13
4Expected Compost Yield= 11.20 kg
5Estimated Maturation Time= 8.0 weeks
6Brown Material to Add for a 30:1 Ratio= 0.00 kg
7Balance Verdict= Too much carbon — decomposition will be very slow, add greens

Assumptions and limits

The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Compost calculated?

Blended ratio = total carbon ÷ total nitrogen; the target is about 30 to 1 Composting works best around a 30 to 1 carbon to nitrogen ratio. Too much nitrogen produces ammonia odour while too much carbon stalls decomposition, and roughly two thirds of the mass is lost as water and carbon dioxide.

Why does Compost matter?

Diverting food waste from landfill avoids methane emissions, which matters more than the compost produced since landfill decomposition is anaerobic.

What values do I need to enter?

This calculator takes 5 inputs: Nitrogen-rich green waste, Carbon-rich brown waste, Carbon to nitrogen ratio of greens, Carbon to nitrogen ratio of browns, Turning interval. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.