Core formula
Estimated emissions = activity amount x emissions factor. For electricity, activity might be kWh. For flights, it might be passenger-kilometers. For fuel, it might be liters or gallons.
CO2e and named entities
CO2e means carbon dioxide equivalent. It converts gases such as methane and nitrous oxide using global warming potential values. IPCC methodology reports and national greenhouse-gas inventories are typical source families for formal work.
Concrete example
If electricity use is 500 kWh and the selected factor is 0.25 kg CO2e per kWh, the estimate is 125 kg CO2e. If another region uses 0.50 kg CO2e per kWh, the same activity estimate doubles to 250 kg CO2e.
What to document
- Source organization.
- Country or grid region.
- Publication year or access date.
- Whether the factor is CO2 or CO2e.
- Whether aviation estimates include non-CO2 effects.
Use the calculators
- Carbon Footprint Calculator
- Flight Emissions Calculator
- Electricity Cost Calculator
- Emissions Estimate Formulas
- CO2e
FAQ
Why does CO2e need a source?
CO2e depends on emissions factors and global warming potential assumptions, which vary by source, region and year.
Can a consumer emissions calculator be used for formal reporting?
Not by itself. Formal reporting needs the required methodology, boundary, factor source and audit trail.
References
- IPCC: National Greenhouse Gas Inventory Programme - Inventory methodology source, accessed 2026-05-15.
- US EPA: Greenhouse Gas Equivalencies Calculator - Public CO2e equivalency reference, accessed 2026-05-15.
Last reviewed: 2026-05-15.