Frequent Questions: EPA’s Greenhouse Gas Equivalencies Calculator
This page answers some of the most commonly asked questions about the Greenhouse Gas Equivalencies Calculator. Click on the questions below to view the answers.
- When I use the calculator to estimate my electricity emissions, the result is very different from what I got last time I used it; what changed?
- What conversion factors are used to generate the calculator’s outputs?
- To what timeframes do the equivalencies refer? For example, does the the “miles driven by an average passenger vehicle” refer to miles driven over one year?
- Which Global Warming Potentials (GWPs) are you using for greenhouse gases in the calculator?
- How can burning 2,000 pounds of coal yield more than 4,000 pounds of carbon dioxide?
- How can it be that the equivalent number of “homes’ energy use for one year” is lower than the equivalent number of “homes’ electricity use for one year?” Home energy use includes electricity, natural gas, LPG, and fuel oil, so shouldn’t the number of homes be higher?
- Why don’t you provide equivalencies in metric units as well as pounds, gallons, miles, etc.?
- I live outside of the United States. Will the calculator work for me?
- How do I calculate the carbon footprint of different food types?
- How do I calculate an ecological footprint?
- How do I calculate average household emissions?
- Can I build my own version of the calculator and post it on my organization’s website?
- Does the calculator have an API?
Assumptions and Sources
When I use the calculator to estimate my electricity emissions, the result is very different from what I got last time I used it; what changed?
In March 2022, EPA updated the Greenhouse Gas Equivalencies Calculator to provide two options for electricity inputs. These options allow users to either 1) estimate emissions from electricity use, or 2) estimate electricity emissions avoided through energy efficiency or renewable energy projects. In either case you should enter a number of kilowatt-hours, but you will get very different results if you choose kilowatt-hours avoided versus kilowatt-hours used.
To estimate emissions from electricity used, the calculator uses a national average emissions factor that includes both baseload and marginal (peaking) power generation. To estimate emissions from electricity avoided, the calculator uses a national average non-baseload emissions factor, because most energy efficiency and renewable energy projects do not affect baseload power generation.
Before March 2022, the calculator provided estimates only for electricity avoided.
What conversion factors are used to generate the calculator’s outputs?
All of the calculations, data sources, and assumptions for EPA’s Greenhouse Gas Equivalencies Calculator are provided on the Calculations and References page.
To what timeframes do the equivalencies refer? For example, does the the “miles driven by an average passenger vehicle” refer to miles driven over one year?
Most of the equivalencies refer only to quantities, rather than quantities over a period of time. The exceptions are easy to identify, since they all include a time frame: for example, “passenger vehicles driven for one year,” “homes’ energy use for one year,” or “coal-fired power plants in one year.”
Which Global Warming Potentials (GWPs) are you using for greenhouse gases in the calculator?
The GHG Equivalencies Calculator is based on the Intergovernmental Panel on Climate Change’s Fifth Assessment Report (2014) GWPs for nearly all equivalencies reported as CO2 equivalents (CO2E). One exception to this is equivalencies that are calculated using the Waste Reduction Model (WARM), which include Coal-fired power plant emissions for one year, GHG emissions avoided by recycling x garbage trucks or railcars full of waste, and Trash bags of waste recycled instead of landfilled, which all use GWPs from the Intergovernmental Panel on Climate Change’s Fourth Assessment Report (AR4) because these are embodied in the WARM tool. To facilitate user reproducibility and transparency, calculations that use data from WARM were not modified to reflect GWPs from AR5. A list of GWP values by gas from AR4 compared to the new ones from AR5 is available below and on the Calculator’s Revision History page.
100 Year GWPs
| Gas | AR4 GWP | AR5 GWP |
|---|---|---|
| CO2 | 1 | 1 |
| CH4 | 25 | 28 |
| N2O | 298 | 265 |
| HFC-23 | 14800 | 12400 |
| HFC-32 | 675 | 677 |
| HFC-125 | 3500 | 3170 |
| HFC-134a | 1430 | 1300 |
| HFC-143a | 4470 | 4800 |
| HFC-152a | 124 | 138 |
| HFC-227ea | 3220 | 3350 |
| HFC-236fa | 9810 | 8060 |
| HFC-43-10mee | 1640 | 1650 |
| R-404A | 3922 | 3943 |
| R-407A | 2107 | 1923 |
| R-407C | 1774 | 1624 |
| R-410A | 2088 | 1924 |
| R-507A | 3985 | 3985 |
| SF6 | 22800 | 23500 |
| CF4 | 7390 | 6630 |
| C2F6 | 12200 | 11100 |
| C4F10 | 8860 | 9200 |
| C6F14 | 9300 | 71900 |
How can burning 2,000 pounds of coal yield more than 4,000 pounds of carbon dioxide?
When coal is burned, the carbon in the coal combines with oxygen to form carbon dioxide. One molecule of carbon dioxide is 3.67 times heavier than a molecule of carbon, due to the additional weight of the two oxygen atoms. Coal is not 100 percent carbon: burning a pound of coal emits 2.07 pounds of CO2. The calculations and sources for this information can be found on the Equivalencies Calculator’s Calculations and References page.
How can it be that the equivalent number of “homes’ energy use for one year” is lower than the equivalent number of “homes’ electricity use for one year?” Home energy use includes electricity, natural gas, LPG, and fuel oil, so shouldn’t the number of homes be higher?
According to the Calculations and References page, each home emits 10.97 metric tons of CO2 per year from all energy use combined, versus 7.27 metric tons of CO2 per year from electricity alone. When an emissions value is entered into the calculator, it calculates the number of households it would take to emit the same amount of CO2 through their overall energy use per year, as well as the number of households it would take to emit the same amount if we consider their electricity use alone. Because the emissions per home are higher when we consider total energy use, it would take fewer homes to emit a given number of metric tons through their total energy use than through their electricity use alone. That’s why the equivalency for the number of homes is smaller for total energy use than for electricity use.
Why don’t you provide equivalencies in metric units as well as pounds, gallons, miles, etc.?
The calculator is designed for use in the United States, and metric units may mislead users into thinking that the equivalencies provided by the calculator are relevant to other countries. As indicated in the Calculations and References page, which presents all the sources, assumptions, and calculations used in the calculator, half of the equivalencies in the calculator are based on US-specific data and would not be accurate outside of the United States.
I live outside of the United States. Will the calculator work for me?
Many of the equivalencies in the calculator are based on US-specific data and will not be accurate outside of the United States. EPA developed the calculator for use in the United States only.
Extending the Calculator
How do I calculate the carbon footprint of different food types?
EPA has not developed a methodology for estimating the life-cycle carbon footprints of food types. The EPA Waste Reduction Model (WARM) includes estimates for emissions associated with food waste, but not for food production and distribution. Documentation for Greenhouse Gas Emission and Energy Factors Used in the Waste Reduction Model (WARM) provides links to studies on life-cycle emissions from a variety of food sources.
How do I calculate an ecological footprint?
Ecological footprints typically include a carbon footprint that represents the area of forest land that would be required to sequester CO2 emissions from human activities. According to the Calculations and References page of EPA's Greenhouse Gas Equivalencies Calculator, one acre of average U.S. forest sequesters 1.06 metric tons of CO2 annually. Using that figure and assuming you have calculated your CO2 emissions, you can estimate the number of acres of forest that would be required to sequester those emissions.
How do I calculate average household emissions?
EPA does not provide an official estimate for average household emissions, but there are two ways you could derive this information from EPA sources:
- EPA’s Inventory of Greenhouse Gas Emissions and Sinks provides a breakdown of emissions by sector, including details for the residential sector. If you divide the total by the number of households in the United States, you will obtain an estimate of residential emissions per household. Note, however, that this does not include transportation. Transportation-related emissions are in Table 2-13. U.S. households own an average of 1.9 vehicles per household.
- EPA’s Household Carbon Footprint Calculator provides values for average emissions from households for specific areas such as vehicles and specific fuels. These values could be built up into an estimate, although note that this does not include sources such as air travel or food. The Household Calculator was designed primarily as an educational tool and does not produce precise estimates.
Can I build my own version of the calculator and post it on my organization’s website?
You may use the calculations to build your own calculator, but please note that EPA updates the calculator periodically (typically annually), so you would need to check back for updates to the conversion factors. The Revision History page documents the changes made in each update.
Does the calculator have an API?
EPA has not developed an API for the Greenhouse Gas Equivalencies Calculator.