Enrichment · Passion Projects · Home and garden

Greens, browns
and the ratio that
makes a pile heat up.

List what goes in the pile by weight. The calculator finds the carbon and nitrogen in each, gives the ratio and moisture of the mix, and tells you how many pounds of leaves or grass would bring it to 30:1.

Check the pileWhat you get

The compost calculator

The worked example is made up: grass, food scraps, leaves and coffee grounds for a school garden bin. Nothing you type leaves this browser.

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What you get

Enrichment · Passion ProjectsFree

What you finish with
The mix’s carbon-to-nitrogen ratio and moisture, carbon and nitrogen from each material, and the pounds of a brown or green to add to reach 30:1. It prints as a summary and downloads as a spreadsheet.
Who it is for
Home and school composters, garden clubs, and students in environmental science and biology.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Passion Projects space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Weigh a bucket of each material once.
  2. Add each material and its weight.
  3. Type lab values if you have them; otherwise leave the typical values.
  4. Read the ratio and moisture, and what to add.
  5. Print the summary and keep it by the bin.

Check the pile

How the ratio is worked out

Dry matter, then carbon over nitrogen.

The worked example: a first fill30 lb grass0.184 lb N30 × 18% dry × 3.4%× C:N 173.12 lb Ccarbon from the grassAll four9.08 ÷ 0.371carbon ÷ nitrogenMix24:1+ 15.4 lb leaves → 30:1The worked example: a first fill30 lb grass0.184 lb N30 × 18% dry × 3.4%× C:N 173.12 lb Ccarbon from the grassAll four9.08 ÷ 0.371carbon ÷ nitrogenMix24:1+ 15.4 lb leaves → 30:1
Wet greens weigh a lot but are mostly water. The ratio comes from the dry matter: carbon and nitrogen are added up across materials, then divided, never averaged.

Why weight and moisture matter

Microbes need about 25 to 30 parts carbon for every part nitrogen. Greens such as grass and food scraps are rich in nitrogen but mostly water; browns such as leaves, straw and cardboard are dry and carbon-rich. So the page first removes the water, then finds each material’s nitrogen and carbon, adds them up and divides. Averaging the ratios themselves would give the wrong answer.

Typical values

Moisture, nitrogen and C:N vary a great deal: grass clippings range from about 9:1 to 25:1 and leaves from 40:1 to 80:1. The values here are typical figures from composting handbooks and extension guides; type a lab result in place of any of them. Below about 25:1 a pile loses nitrogen as ammonia; above about 40:1 it works slowly.

Sources

  1. Rynk, R. (Ed.). (1992). On-Farm Composting Handbook (NRAES-54). Natural Resource, Agriculture, and Engineering Service: appendix A, characteristics of raw materials.
  2. Cornell Waste Management Institute. Composting: the science and engineering of composting, C:N ratio calculations (compost.css.cornell.edu).
  3. U.S. Environmental Protection Agency. Composting at home (epa.gov).
  4. Penn State Extension. Composting for the home gardener (extension.psu.edu).

The worked example is made up. Typical values are estimates; your materials will differ. Your figures stay in this browser. Support: team@caveatacademic.com.