Carbon Accounting Essentials
GHG Protocol Fundamentals

Calculation Example

May 28, 2024
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Calculation Example

Let's connect the dots by looking at an example.

Suppose a utility bill shows a usage of 10,000 standard cubic feet (SCF) of natural gas.

As we said earlier, the combustion of natural gas emits three greenhouse gasses:

  • Carbon dioxide
  • Methane
  • Nitrous oxide

For this example, the following three emissions factors are required for the three emitted GHGs:

  • 53.06 kg CO2/mmBtu
  • 0.001 kg CH4/mmBtu
  • 0.0001 kg N2O/mmBtu

To calculate emissions, the amount of natural gas must be multiplied by each emissions factor.

But first...

Our activity data is in standard cubic feet and the emission factors are in mmBtu.


So the first step is to convert the activity data into the same units as the emission factors.
We do this by multiplying the activity data by a conversion factor.

Activity Data Conversion Factor* Activity Data in mmBtu
10,000 SCF x 0.001026 mmBtu / SCF = 10.26 mmBtu
*The conversion factor is provided by the EPA


Now the activity data can be multiplied by each emission factor. The mmBtu units cancel out, leaving only greenhouse gas emissions.

Activity Data Emission Factor GHG Emissions
10.26 mmBtu x 53.06 kg CO2 / mmBtu = 544.400 kg CO2
10.26 mmBtu x 0.001 kg CH4 / mmBtu = 0.010 kg CH4
10.26 mmBtu x 0.0001 kg N2O / mmBtu = 0.001 kg N2O

We now have quantities of each greenhouse gas emitted due to the footprint activity (burning natural gas). Unfortunately, we can’t simply add the three numbers together to come up with a total emissions. Each of these greenhouse gasses is not equal in terms of its impact on global warming.

In order to correctly total these three emissions quantities,  they must first be converted into a common unit of carbon dioxide equivalent (or CO2e). This is accomplished by multiplying each quantity by its global warming potential (GWP).

GHG Emissions GWP CO2e
544.40 kg CO2 x 1 = 544.40 kg CO2e
0.01 kg CH4 x 25 = 0.25 kg CO2e
0.001 kg N2O x 298 = 0.298 kg CO2e
Because the GWP value of CO2 is 1, the amount is the same when it is converted to CO2e

Now that each of the emissions is in a common unit of CO2e, they can be totaled to provide a single value representing the greenhouse gas that was emitted as a result of the original footprint activity (combusting 10,000 SCF of natural gas).

544.400 kg CO2e
+ 0.250 kg CO2e
+ 0.298 kg CO2e
= 544.948 CO2e

So, to recap...

This is our complete calculation:

This calculation is intended as an example and numbers may be off due to rounding.

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