EPA estimate: ~650 lbs/yr food waste & ~500 lbs/yr yard trimmings per household. Use these estimates
Composting CO₂ Savings Calculator
See how much greenhouse gas you save by composting food scraps and yard waste instead of landfilling — built on EPA WARM v16 emission factors, with the methodology laid out in full.
How Composting Reduces Greenhouse Gas Emissions
Bury food scraps in a landfill and they break down anaerobically — no oxygen down there — which means they throw off methane (CH₄), a gas that traps heat about 25 times more effectively than CO₂ over a 100-year stretch (that's the IPCC AR4 GWP figure). Compost the same scraps and you get aerobic decomposition instead: CO₂ and water, not methane. The gap between the two is real — the EPA WARM v16 model puts composting food waste at 0.72 metric tons of CO₂ equivalent (MTCO₂e) avoided per short ton, compared to sending it to the landfill. [1]
Do the math for an average U.S. household composting about 650 lbs of food scraps a year, and you land around 0.23 MTCO₂e avoided — roughly what you'd emit driving 570 miles, or running a typical home's lights for about three months. Scale that across the country: if every U.S. household composted its food waste, we're talking about 35 million metric tons of CO₂e avoided annually — the same as pulling 7.5 million cars off the road for a year.
Food Waste vs. Yard Trimmings: Why the Factors Differ
One thing that trips people up in the EPA WARM model: food waste (0.72 MTCO₂e/ton) and yard trimmings (0.03 MTCO₂e/ton) get wildly different composting factors — a 24× gap. Here's why. Yard trimmings carry more lignin and cellulose than food scraps, and those materials barely budge in an anaerobic landfill. Slower decomposition means less methane gets generated in the first place, so the landfill baseline for yard waste is already fairly low — which leaves less room for composting to improve on it.
That doesn't make yard waste composting pointless — it still keeps material out of landfills, cuts down on hauling costs, and gives you usable soil amendment at the end. The payoff just leans more toward diversion and finished compost than toward methane avoided.
Methodology Notes: GWP and WARM Model Limitations
EPA WARM v16 runs on a methane GWP of 25, pulled from the IPCC's Fourth Assessment Report (AR4). The newer Sixth Assessment Report (AR6, 2021) bumps that figure to 27.9 over 100 years — or 80.8 if you look at the 20-year window. Swap in the AR6 number and the food waste composting benefit comes out about 12% higher than what WARM v16 reports. This calculator sticks with WARM v16 factors, since that's what matches EPA's official reporting.
Worth flagging: WARM doesn't capture the full lifecycle benefit of putting compost back into soil — things like carbon sequestration, less demand for synthetic fertilizer (and the emissions that come with making it), and better water retention that cuts irrigation energy. So the real climate benefit of composting is probably higher than what WARM reports here. For the full rundown of model assumptions, see EPA's WARM FAQ.
Composting CO₂ Savings FAQ
How much CO₂ does composting save per year?
For an average household composting about 650 lbs of food scraps a year, that works out to roughly 0.23 MTCO₂e saved — about the same as driving 570 miles. That's based on EPA WARM v16 factors: 0.72 MTCO₂e per short ton for food waste, 0.03 for yard trimmings.
Why does composting yard waste save less CO₂ than food waste?
Yard trimmings break down slowly in landfills — high lignin content means low methane yield — so the landfill baseline is already fairly clean. Food waste, on the other hand, decomposes fast and throws off a lot of methane, which is exactly what composting sidesteps. Per EPA WARM v16: food comes in at 0.72 MTCO₂e/ton versus 0.03 for yard trimmings.
What GWP does EPA WARM use for methane?
WARM v16 uses a GWP of 25 for methane, from IPCC AR4. The newer AR6 assessment updates that number to 27.9. Apply AR6 instead, and food waste composting benefits come out roughly 12% higher than what WARM v16 reports.
How much food waste does a household produce per year?
EPA puts the average U.S. household at about 650 lbs of food waste a year, though actual numbers swing from 200–1,200+ lbs depending on household size, diet, and shopping habits. Food makes up around 24% of U.S. municipal solid waste by weight.