Methodology

Composting Calculator Data Sources & Methodology

Every number on compost.tools traces back to a citable source. Here you'll find every primary source we use, the places where authorities disagree, and how we decide which value to show.

Primary-source citations Disagreement table Formula notes

Last reviewed: April 2026

Data Hierarchy

When sources conflict, here's the order we lean on:

1
University cooperative extension publications: Peer-reviewed, regionally tested, written for practical application. Primary sources: Cornell, NC State, Oregon State, Penn State, Nebraska, Clemson, UAF, and UMD.
2
USDA and EPA datasets: NRCS National Engineering Handbook Part 637, EPA WARM model, USDA AMS organic compost guidance.
3
On-Farm Composting Handbook (NRAES-54): The field standard since 1992, edited by Robert Rynk at Cornell. Still the most comprehensive single reference for composting data.
4
CREF Appendix B: The US Composting Council Research & Education Foundation maintains an updated feedstock database that incorporates newer data than NRAES-54.
5
Peer-reviewed literature: Used to fill gaps not covered by extension sources.

Known Source Disagreements

The composting literature doesn't always agree with itself. When authoritative sources clash, we don't just quietly pick one, we show you the disagreement and explain why we went the way we did.

Topic Source A Value A Source B Value B What compost.tools uses Rationale
Optimal composting moisture Cornell Waste Management Institute; most extension 50–60% NC State AG-593 Table 1 40–65% reasonable; 50–60% preferred 40–65% acceptable; 50–60% target shown Both sources agree on 50–60%. The calculators treat 40–65% as workable, flag the 50–60% target, and call anything above 65% too wet (AG-593: exceeding 65% goes anaerobic).
Worm consumption rate UMD Extension, OSU EM-9034 1× body weight/day (ideal) UAF, Clemson 0.5× body weight/day 0.5× as practical default; 1× shown as ideal-conditions maximum Clemson and UAF describe typical home bins. UMD and OSU give 1× as a maximum (OSU: "as much as its own body weight"), reached only under optimal conditions (60–75°F, fully established bin, ideal feed).
Methane GWP multiplier EPA WARM v16 (IPCC AR4 2007) GWP-100 = 25 IPCC AR6 (2021) GWP-100 = 27.9; GWP-20 = 81 WARM value (25) as auditable standard; AR6 20-yr (81) shown as note EPA WARM is the regulatory/auditing standard in the US. AR6 values shown transparently so users can understand the higher-impact scenario.
Lawn topdressing max depth Penn State Extension A thin layer of about ¼" worked in after core aeration; ½" only when tilled into bare soil Common turf-care practice Up to ½" on established turf ¼" recommended; ½" upper limit on aerated turf; warning shown beyond ½" Penn State Extension's cited topdressing rate is about ¼". Depths above ½" can smother grass crowns.
Container compost percentage NC State Extension AG-593 15–40% UMD container media guidance Up to 100% for some applications 30% default; 5–50% range; warn above 40% Higher percentages require mature, low-salt, stable compost. NC State's 15–40% is appropriate for typical bagged composts. UMD's 100% applies to professionally-made finished compost.
C:N optimal starting ratio Cornell Waste Management Institute ~30:1 NC State AG-593 25:1–35:1 as target range 25–35:1 as target range; color code: green 25–35, amber 20–25 or 35–50, red otherwise A range is more defensible than a single point. Piles from 25–35:1 decompose actively; outside this range shows diminishing efficiency, not failure.

Primary Sources

  1. Rynk, R. (Ed.). (1992). On-Farm Composting Handbook (NRAES-54). Northeast Regional Agricultural Engineering Service, Cornell University. Available via Cornell eCommons. The primary reference for C:N ratios, bulk density, and moisture content used throughout the feedstock database.
  2. US Composting Council Research & Education Foundation (CREF). (2021). Appendix B: Typical Characteristics of Common Feedstocks. compostfoundation.org/B/. Updated feedstock database; primary supplement to NRAES-54 for materials not covered in the 1992 edition.
  3. Cornell Waste Management Institute. Cornell Composting. C/N Ratio, Compost Chemistry, Compost Physics and Compost Microorganisms. Mixture C:N formula and the 30:1 starting target; 50–60% moisture optimum; microbial die-off above about 65°C.
  4. NC State Extension. (2025, rev.). AG-593: Large-Scale Organic Materials Composting. content.ces.ncsu.edu. C:N target ranges and moisture guidance.
  5. OSU Extension. (2025). EM-9217: Interpreting Compost Analyses. extension.oregonstate.edu. PAN and nutrient analysis framework for the compost value calculator.
  6. Penn State Extension. (1997). Using Composts to Improve Turf Performance. extension.psu.edu. Topdressing rate: a thin layer of about ¼" worked in after core aeration; ½" only when tilled into bare soil.
  7. Nebraska Extension. (2013). G2222: Garden Compost. University of Nebraska–Lincoln. extensionpubs.unl.edu. Compost share of soil mixes for containers, raised beds and ground beds: 10% minimum, 30% optimum, 50% maximum. Hot-pile dimensions: at least 3 × 3 × 3 ft (1 cubic yard), at most 5 ft tall × 5 ft wide.
  8. USDA NRCS. (2010). National Engineering Handbook Part 637 Chapter 2: Composting. USDA NRCS. Manure feedstock data; large-scale composting parameters.
  9. USDA National Organic Program. 7 CFR 205.203(c): Soil fertility and crop nutrient management practice standard. law.cornell.edu. Compost rules for organic production: initial C:N of 25:1–40:1; 131–170°F for 3 days (in-vessel or static aerated pile) or 15 days with at least 5 turnings (windrow). Raw manure under (c)(1): incorporated at least 120 days before harvest when the edible portion touches the soil, 90 days otherwise. Cited in the pile temperature calculator and the can-and-cannot guide.
  10. EPA. (2023). Waste Reduction Model (WARM) v16. epa.gov/warm. GHG emission factors used in CO₂ savings calculator: food waste net avoided ≈ 0.65 MTCO₂e/short ton (Exhibit 1-10: landfilling +0.50, composting −0.15); yard trimmings 0.03 MTCO₂e/short ton is a site estimate: WARM v16 Exhibit 2-4 scores composting yard trimmings at −0.05 and landfilling them at −0.20, i.e. no net saving.
  11. EPA. (2018). National Overview: Facts and Figures on Materials, Wastes and Recycling. epa.gov. Per-capita food waste and yard waste baseline estimates.
  12. EPA. (1993). Appendix B to 40 CFR Part 503: Pathogen Treatment Processes. law.cornell.edu. PFRP temperature and time requirements: 131°F (55°C) for 3 days (in-vessel or static aerated pile) or 15 days with at least 5 turnings (windrow).
  13. Clemson Extension. HGIC 1607: Worm Composting. hgic.clemson.edu. Bin sizing and feeding rate guidance; 0.5× body weight/day practical limit.
  14. OSU Extension. EM-9034: Composting with Worms. extension.oregonstate.edu. Population growth: doubling in about 60 days under good conditions; a red wiggler can eat as much as its own body weight a day; bin construction and management guidance.
  15. University of Maryland Extension. Indoor Worm Composting or Vermicomposting. extension.umd.edu. 1× body weight/day under ideal conditions (noted as maximum, not typical).
  16. University of Maryland Extension. Growing Media (Potting Soil) for Containers. extension.umd.edu. Suggested container mixes include 50% soilless mix + 50% compost, and 100% compost.
  17. UAF Cooperative Extension. Composting with Worms. uaf.edu/ces. Bin sizing rule-of-thumb and home-bin reproduction guidance.
  18. NC State Extension. Herbicide Carryover in Hay, Manure, Compost, and Grass Clippings. content.ces.ncsu.edu. Aminopyralid, clopyralid, and picloram persist through grazing and composting and injure sensitive crops. Cited in the can-and-cannot guide.
  19. US FDA. Authorized Uses of PFAS in Food Contact Applications. fda.gov. PFAS grease-proofing agents on paper and paperboard food packaging and their 2024 US market phase-out. Cited in the can-and-cannot guide.
  20. Biernbaum, J. A. (2015). Vermicomposting and Vermiculture Systems for Cold Climates. Michigan State University, Department of Horticulture. canr.msu.edu. Worm compost output per bed area (0.5–1 cubic yard per 25 sq ft bed per year), realistic feeding rate per square foot, and manure-to-vermicompost recovery figures.
  21. Sherman, R. (2003). EBAE 103-83: Raising Earthworms Successfully. North Carolina Cooperative Extension. extension.rwfm.tamu.edu. Wedge and windrow harvest interval; continuous-flow reactor stocking rate and harvesting.
  22. EPA. Composting At Home. epa.gov. Two to three parts browns to one part greens; a pile left untended may take a year; a cured pile shrinks to about one-third of its original size.
  23. EPA. Approaches to Composting. epa.gov. The ideal ratio of roughly three parts browns to one part greens by volume; three-bin systems as a common model.
  24. LSU AgCenter. (2022). Pub. 3838-K: Composting Series: Three-Bin System. lsuagcenter.com. Minimum 3 × 3 × 3 ft for each bin; fill and turn the first bin weekly, hold the second until it cools to near ambient, finish and cure in the third.

Formula References

C:N Ratio Blending (Model A: dry-mass weighted harmonic mean):

D_i = Volume_i × BulkDensity_i × (1 − Moisture_i)
R_mix = (Σ D_i) / (Σ D_i / R_i)
Moisture_mix = Σ(Volume_i × BulkDensity_i × Moisture_i) / Σ(Volume_i × BulkDensity_i)

Source: Cornell Waste Management Institute. The harmonic mean is mathematically correct for blending ratios. Simple arithmetic averaging of C:N ratios is a common error that produces incorrect results.

Moisture Content (oven-dry method):

MC% = ((Wet_Weight − Dry_Weight) / Wet_Weight) × 100

Water to Add:

W_add = W_pile × (m_target − m_current) / (1 − m_target)

Where m values are moisture fractions (0–1). Source: NRAES-54 Chapter 4.

Compost Bin Size:

V_week = (W_scraps / D_scraps) × (1 + R_browns) + V_yard
Hot:  3 bins, each ≥ 3 × 3 × 3 ft (27 cu ft), ≤ 5 ft tall × 5 ft wide; Weeks_batch = 27 / V_week
Cold: 1 bin holding V_year = 52 × V_week, shrinking to about V_year / 3 once cured

D_scraps is the typical bulk density of mixed food scraps (42 lb/cu ft, NRAES-54 / CREF, read from our feedstock data) and R_browns is 3 or 2 parts browns per part scraps by volume. V_yard is added as entered: the ratio covers kitchen scraps only, so green yard material should be entered with its browns. Sources: Nebraska Extension G2222 (pile dimensions), LSU AgCenter 3838-K (three-bin rotation), and the EPA's Composting At Home and Approaches to Composting (browns ratio, a year for an untended pile, one-third shrinkage). The page shows no composting time for hot piles, because the sources disagree on it.

Limitations

The C:N ratios, moisture contents, and bulk densities in our feedstock database are representative ranges from published literature. Actual values vary substantially depending on:

If you're composting commercially or under regulation, get a lab analysis of your specific feedstocks. Your state university's cooperative extension service often runs subsidized soil and compost testing, worth a call.