EPA estimate: ~650 lbs/yr food waste & ~500 lbs/yr yard trimmings per household. Use these estimates
Composting CO₂ Savings Calculator
Estimate the greenhouse gas savings from composting food scraps and yard waste — using EPA WARM v16 emission factors with full methodology notes.
How Composting Reduces Greenhouse Gas Emissions
When food scraps go to a landfill, they decompose anaerobically — without oxygen — and produce methane (CH₄), a greenhouse gas 25 times more potent than CO₂ over a 100-year period (IPCC AR4 GWP). Composting instead creates aerobic decomposition, releasing CO₂ and water rather than methane. The difference is substantial: the EPA WARM v16 model calculates that composting food waste avoids 0.72 metric tons of CO₂ equivalent (MTCO₂e) per short ton compared to landfilling. [1]
For the average U.S. household composting about 650 lbs of food scraps per year, that's approximately 0.23 MTCO₂e avoided — equivalent to driving roughly 570 miles or running a typical home's lights for about 3 months. Scaled up: if every U.S. household composted its food waste, the annual GHG reduction would be approximately 35 million metric tons CO₂e — equivalent to removing 7.5 million cars from the road for a year.
Food Waste vs. Yard Trimmings: Why the Factors Differ
A notable feature of the EPA WARM model is the large difference between food waste (0.72 MTCO₂e/ton) and yard trimmings (0.03 MTCO₂e/ton) composting factors — a 24× difference. This surprises many users. The explanation is that yard trimmings contain more lignin and cellulose than food waste — materials that decompose very slowly in landfills under anaerobic conditions. Because slow decomposition means less methane generated, the baseline (landfill) scenario for yard waste is already relatively low in emissions, so the benefit of composting it instead is smaller.
This doesn't mean yard waste composting is unimportant — it still diverts material from landfills, reduces transportation costs, and produces useful soil amendment. The environmental benefit just comes more from waste diversion and compost production than from methane avoidance.
Methodology Notes: GWP and WARM Model Limitations
EPA WARM v16 uses a methane GWP of 25 (IPCC Fourth Assessment Report, AR4). The newer IPCC Sixth Assessment Report (AR6, 2021) updates CH₄ GWP to 27.9 over 100 years (or 80.8 over 20 years). If AR6 values were used, the food waste composting benefit would be approximately 12% higher than the WARM v16 estimate. The calculator uses WARM v16 factors to match EPA official reporting.
WARM also does not account for the full lifecycle benefit of compost application to soil — including soil carbon sequestration, reduced synthetic fertilizer production (and its GHG footprint), and improved soil water retention reducing irrigation energy use. The actual climate benefit of composting is likely higher than the WARM model captures. See EPA's WARM FAQ for detailed model assumptions.
Composting CO₂ Savings FAQ
How much CO₂ does composting save per year?
An average household composting ~650 lbs of food scraps saves about 0.23 MTCO₂e per year — equivalent to driving ~570 miles. Using EPA WARM v16 factors (0.72 MTCO₂e/short ton food, 0.03 MTCO₂e/short ton yard trimmings).
Why does composting yard waste save less CO₂ than food waste?
Yard trimmings decompose slowly in landfills (high lignin content, low methane yield), so the baseline landfill emissions are already low. Food waste decomposes quickly and generates significant methane — which composting avoids. EPA WARM v16: food 0.72 MTCO₂e/ton vs. yard 0.03 MTCO₂e/ton.
What GWP does EPA WARM use for methane?
WARM v16 uses GWP = 25 for methane (IPCC AR4). IPCC AR6 updates this to 27.9. If AR6 values applied, food waste composting benefits would be about 12% higher than WARM estimates.
How much food waste does a household produce per year?
EPA estimates ~650 lbs/household/year for U.S. households, though actual amounts range from 200–1,200+ lbs depending on household size, diet, and food purchasing habits. About 24% of U.S. municipal solid waste by weight is food.