Measuring corporate greenhouse gas (GHG) emissions is the first step toward reducing them. This calculator applies the GHG Protocol Corporate Standard — the globally accepted framework used by over 92% of Fortune 500 companies — to estimate your organization's Scope 1, 2, and 3 footprint in metric tonnes of CO₂ equivalent (t CO₂e) per year.

Why the GHG Protocol's three-scope framework matters

The GHG Protocol divides emissions into three scopes to prevent double-counting and to draw a clear boundary between what a company directly controls versus what it influences. Scope 1 covers direct combustion (natural gas furnaces, company-owned vehicles) — the emissions you own completely. Scope 2 covers purchased electricity, where the emissions occur at a power plant but you drive the demand. Scope 3 covers everything else: business flights, employee commuting, and the embedded carbon in your supply chain spend.

Most companies discover that Scope 3 is their largest source. A technology firm with a lean office may find that business travel and supplier emissions represent 70–80% of their total footprint. For manufacturers, Scope 1 gas combustion often dominates. Knowing which scope is largest tells you where to direct decarbonization investment.

Emission factors and data sources

Each activity is converted to CO₂e using an emission factor — a published coefficient from authoritative sources. This calculator uses:

  • Natural gas: 0.00531 t CO₂e per therm (EPA 40 CFR Part 98, Subpart C)
  • Vehicle fleet: 0.000404 t CO₂e per mile (EPA average light-duty fleet, 2022)
  • Electricity: Regional eGRID 2022 factors, ranging from 0.080 kg/kWh (Northwest hydro) to 0.450 kg/kWh (Midwest coal-heavy)
  • Air travel: 0.000255 t CO₂e per passenger-mile (UK DEFRA 2023, economy radiative forcing included)
  • Supply chain: $65 per t CO₂e intensity factor (US EPA supply-chain emission factors, 2022)

Emission factors change over time as the grid cleans up and vehicle fleets electrify. The EPA updates eGRID annually; revisit your calculation each year to capture grid improvements.

Limitations and when to seek specialist help

This calculator provides a screening-level estimate suitable for internal target-setting, sustainability reports, and identifying where to focus reduction efforts. It is not a substitute for a third-party verified GHG inventory if your organization needs to publish figures for CDP, GRI, TCFD, or CSRD compliance, or if you are making carbon credit claims.

Key limitations to be aware of:

  • Supply chain: The spend-based Scope 3 method has ±50% uncertainty; supplier-specific data (Scope 3 Category 1) is much more accurate but requires engagement with your suppliers.
  • Refrigerants: Fugitive emissions from air conditioning and refrigeration (Scope 1 F-gases) are not modeled here — these can be significant for food, pharma, and cold-chain logistics businesses.
  • Process emissions: Industrial processes like cement calcination, chemical reactions, or waste treatment require sector-specific emission factors not included in this tool.
  • Grid factor timing: Market-based accounting (using renewable energy certificates or power purchase agreements) can reduce your reported Scope 2 to zero, whereas this calculator uses location-based factors only.