How much CO₂ does natural gas emit?
Burning natural gas releases about 53.1 kg of CO₂e per million Btu, which is 5.31 kg per therm, 5.45 kg per 100 cubic feet, 0.182 kg per kWh or 2.03 kg per cubic metre (US EPA; UK government). That is about 44% less than coal and 28% less than heating oil for the same energy. Producing and delivering the gas adds roughly another 17%, and methane leaking along the way can add considerably more: measured US leak rates of 2.3–2.4% of production warm about 31% as much as the burned gas’s CO₂ over 100 years.
Natural gas is the cleanest-burning fossil fuel, but it is still a fossil fuel, and its footprint does not end at the burner. This page gives the official emission factors for every common unit, compares gas with coal and oil, and sets out what measurements of methane leaks from the gas supply chain add.
CO₂ per unit of gas
| Unit | kg CO₂e | Source |
|---|---|---|
| Million Btu (MMBtu) | 53.11 | US EPA, 2025 |
| Therm (100,000 Btu) | 5.31 | US EPA, 2025 (our conversion) |
| Cubic foot | 0.0545 | US EPA, 2025 |
| 100 cubic feet (Ccf) | 5.45 | US EPA, 2025 (our conversion) |
| kWh (gross calorific value) | 0.182 | UK DEFRA, 2026 |
| Cubic metre | 2.026 | UK DEFRA, 2026 |
US bills are usually in therms or hundreds of cubic feet; UK and European bills in kWh, worked out from cubic metres. The two governments’ factors agree closely: the EPA’s comes to 0.181 kg per kWh against DEFRA’s 0.182. To convert between units, use the m³ to kWh, kWh to therms and m³ to kg converters.
Where the CO₂ comes from
Natural gas is mostly methane, CH₄. Burning it joins each carbon atom to two oxygen atoms, so every kilogram of methane burned makes 2.75 kg of CO₂ (the ratio of their molecular weights, 44 to 16). Carbon dioxide is 99.9% of the EPA factor; the rest is a little unburned methane and nitrous oxide. The natural gas glossary entry sets out the three gases, the gross and net calorific value bases, and how LNG and biomethane differ, and the natural gas combustion methodology shows how to calculate a company’s emissions from meter readings.
Natural gas compared with other fuels
| Fuel | kg CO₂e per MMBtu | Natural gas compared |
|---|---|---|
| Natural gas | 53.1 | — |
| Propane | 63.1 | 16% less |
| Petrol (motor gasoline) | 70.5 | 25% less |
| Heating oil (distillate no. 2) | 74.2 | 28% less |
| Bituminous coal | 94.0 | 44% less |
| Anthracite coal | 104.4 | 49% less |
For the same heat, natural gas emits a little over half as much as coal, because methane carries four hydrogen atoms for each carbon, and burning the hydrogen releases energy without making CO₂. That is why gas has replaced coal in so many power stations. It is not low-carbon, though: a heat pump running on the average US grid emits less than a gas furnace for the same heat, as the guide to reducing your home’s carbon footprint works out.
Before it reaches you: production and leaks
The factors above count only the burning. Extracting, processing and piping the gas also emit: DEFRA puts these upstream (well-to-tank) emissions at 0.030 kg CO₂e per kWh, about 17% on top of combustion.
Measurements suggest methane leaking from wells, pipelines and compressors is larger than official inventories assume. Methane traps far more heat than CO₂: over 100 years, a tonne of fossil methane warms about 29.8 times as much as a tonne of CO₂, and over 20 years about 82.5 times (IPCC AR6 values).
| Study | Loss rate | Compared with the official inventory |
|---|---|---|
| Alvarez et al. 2018, Science (2015 emissions) | 2.3% of gross production | About 60% higher (13 against 8.1 million tonnes of methane a year) |
| Sherwin et al. 2024, Nature (six regions, aerial surveys) | 2.43% average; 0.71% to 9.77% by region | About three times higher |
Alvarez and colleagues worked out what their leak rate means for the gas that is burned: over 20 years, the leaked methane warms about as much as the CO₂ from burning the gas, and over 100 years about 31% as much. Leak rates vary enormously, from under 1% in a productive gas region to nearly 10% in a fast-growing oil-focused one, and in many of the surveys a small fraction of well sites (under 2%) produced most of the well-site emissions. These are US measurements; other countries’ supply chains differ. Sherwin’s study was corrected in 2026; the figures here are from the corrected version, which its authors say does not change the main results.
Electricity from natural gas
Over their whole life, including building the plant and supplying the fuel, combined-cycle gas power stations emit a median of 490 g CO₂e per kWh of electricity in the IPCC’s review and 486 g in the US National Renewable Energy Laboratory’s, against 820 and 1001 g for coal. In the same IPCC review, wind, solar and nuclear power emit between about 10 and 50 g; see the carbon footprint of nuclear power for every source compared.
Frequently asked questions
About 53.1 kg of CO₂e per million Btu when burned, or 5.31 kg per therm, 5.45 kg per 100 cubic feet, 0.182 kg per kWh and 2.03 kg per cubic metre, according to the US EPA and the UK government.
About 5.31 kg of CO₂e, from the EPA’s 53.11 kg per million Btu (a therm is 100,000 Btu). Producing and delivering the gas adds more upstream.
When burned, yes: about 53.1 kg of CO₂e per million Btu against 94.0 for bituminous coal, roughly 44% less. For electricity over the whole life cycle, gas plants emit around 490 g per kWh against 820 to 1,000 g for coal. Methane leaks narrow the gap, especially over shorter time horizons.
Measured US leak rates are around 2.3% to 2.4% of gas produced. At that rate, Alvarez et al. (2018) found the leaked methane warms about 31% as much as the CO₂ from burning the gas over 100 years, and about as much over 20 years.
A cubic metre of natural gas holds about 11 kWh of energy (gross calorific value), so the factor per cubic metre is roughly 11 times the factor per kWh. Gas suppliers convert your meter reading from cubic metres or cubic feet to kWh or therms using the gas’s measured energy content.
Sources: US EPA, GHG Emission Factors Hub (2025); DEFRA/DESNZ, Greenhouse gas reporting: conversion factors 2026; Alvarez, R. A. et al. (2018), “Assessment of methane emissions from the U.S. oil and gas supply chain”, Science 361, 186–188; Sherwin, E. D. et al. (2024), “US oil and gas system emissions from nearly one million aerial site measurements”, Nature 627, 328–334 (corrected 2026); IPCC AR5 WGIII Annex III; NREL (2021) life-cycle harmonisation. Related: natural gas · natural gas combustion methodology · natural gas emission factor API