About compost.tools

What This Is

compost.tools is a collection of 10 free calculators that help you make better composting and soil amendment decisions. Every calculator is based on research from USDA, university cooperative extension services, and the US Composting Council Research & Education Foundation's CREF feedstock database — the same sources professionals use.

The site was built by a composter who got frustrated searching through PDF extension guides every time they needed to figure out how much compost to add to a raised bed, or whether their pile's C:N ratio was in range. These calculators do the math so you can focus on the pile.

Data Philosophy

Every number in every calculator traces to a citable source. We use a strict hierarchy:

• University cooperative extension publications — peer-reviewed, regularly updated, written for practical use
• USDA and EPA datasets — NRCS NEH Part 637, EPA WARM model
• On-Farm Composting Handbook (NRAES-54) — the field standard since 1992
• CREF Appendix B — the US Composting Council's regularly-updated feedstock database

Where authoritative sources disagree — which happens more often than you'd expect — we show both values and explain our choice. We do not silently pick the number that "sounds right." See the full methodology and citations page for every source and a table of known disagreements.

Transparency on Limitations

Composting is governed by living systems, not equations. The C:N ratios in our feedstock database are representative ranges, not universal constants — the same grass clippings can range from 9:1 to 25:1 depending on fertilization history, growth stage, and moisture. Our calculators give you a defensible starting point, not a guarantee.

For commercial or regulated composting operations, we strongly recommend getting a laboratory analysis of your feedstocks from a certified soil lab. University extension services in every state offer subsidized testing.

Units

All calculators support both US customary and metric units. Your preference is saved in your browser's local storage and persists between visits. First-time visitors outside the US, Liberia, and Myanmar default to metric based on browser locale.

No Account Required

compost.tools requires no registration, no login, and no email address. All calculations run in your browser. No data about your inputs is sent to our servers.

Advertising

The site is supported by Google AdSense advertising. Ads only load if you click "Accept all" in the cookie banner — no ads are served until you explicitly consent. Anonymized analytics (GA4) runs by default outside the EEA, UK, and Switzerland, where you can opt out any time with the "Reject" button; within the EEA, UK, and Switzerland it sets no cookies until you accept (only anonymized, cookieless measurement until then). Clicking "Reject" sets no analytics or advertising cookies and removes any already set. See the privacy policy for details.