What is the difference between the three scopes?

Scope 1 is direct emissions from sources you own or control, like company vehicles and boilers. Scope 2 is indirect emissions from the electricity and heat you buy. Scope 3 is all other indirect emissions across your value chain, which is usually the largest share.

Why is Scope 3 often the biggest?

Scope 3 covers your entire supply chain, product use, business travel, commuting, and waste. For most service and retail companies it dwarfs Scopes 1 and 2 combined, frequently making up 70 to 90 percent of the total inventory.

How accurate is a spend-based estimate?

Spend-based Scope 3 factors convert money spent on goods into emissions using economic averages. They are useful for a first screening but coarse — a supplier-specific or activity-based method is far more accurate and is needed for credible target-setting.

Does this follow the GHG Protocol?

It mirrors the GHG Protocol's scope structure and uses public emission factors, but it is a simplified screening tool. A reportable inventory requires a defined organisational boundary, complete activity data, and verification against the standard.

What units should I enter?

Fuel in litres, natural gas in cubic metres, electricity and heat in kWh, travel in passenger-kilometres, procurement in your currency, and waste in tonnes. The tool converts each to tonnes CO2e using the matching factor.

What is the Scope 1 / 2 / 3 GHG Emissions Estimator?

Enter activity data for direct combustion (Scope 1), purchased electricity and heat (Scope 2), and the main Scope 3 categories — travel, supply chain, waste, commuting — to produce a GHG inventory summary in tonnes CO2e. For sustainability leads and CFOs. It runs free in your browser on Gera Tools, with nothing uploaded.

Scope 1 / 2 / 3 GHG Emissions Estimator

Name: Scope 1 / 2 / 3 GHG Emissions Estimator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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This estimator assembles a company-level greenhouse-gas inventory across the three scopes defined by the GHG Protocol. You enter activity data — fuel burned, energy purchased, travel taken, goods bought — and each line is multiplied by a public emission factor and summed into a tonnes-CO2e total with a per-scope breakdown. It is intended for a first screening inventory and ESG report preparation.

What the three scopes cover

Understanding what each scope includes is as important as the number it produces:

Scope 1 — Direct emissions come from sources you own or control: combustion of fuel in company vehicles, boilers, and generators. These are the most straightforward to measure because you have direct records.

Scope 2 — Indirect energy emissions come from the electricity and heat you purchase from the grid. You do not combust the fuel — the power station does — but your purchase drives the demand. Two reporting methods exist: location-based (grid average factor) and market-based (certificates and supplier factors). This estimator uses a location-based approach.

Scope 3 — Value chain emissions cover everything else: business travel by non-company vehicles, employee commuting, purchased goods and services, waste, and downstream use of your products. For most service companies, Scope 3 is 70–90% of the total inventory.

How it works

Each activity is converted with its own factor and the scopes are summed:

Scope 1 = diesel·L×2.51 + petrol·L×2.31 + gas·m3×2.04   (kg CO2e)
Scope 2 = electricity·kWh×0.21 + heat·kWh×0.19
Scope 3 = airTravel·pkm×0.18 + railTravel·pkm×0.035
        + procurementSpend×0.30 + waste·t×450 + commuting·pkm×0.17
total   = (Scope1 + Scope2 + Scope3) / 1000   (tonnes CO2e)

Factors are public averages (DEFRA / IEA grid intensities). The procurement line uses a spend-based factor of roughly 0.30 kg CO2e per currency unit — a deliberately coarse screening proxy. For a credible supplier engagement program, replace it with activity-based or supplier-specific data.

Worked example and where to focus

A small office burning 2,000 L of company-car diesel, buying 40,000 kWh of grid electricity, flying 50,000 passenger-km, and spending 200,000 on goods produces roughly 75 tonnes CO2e — with Scope 3 (travel plus procurement) accounting for the large majority. That pattern is typical.

Where reductions have the most impact:

Flights: air travel has one of the highest per-km factors. Substituting one long-haul return flight with a video call typically removes more emissions than all office energy improvements combined.
Procurement: engaging your top-spend suppliers on emissions data and switching to lower-carbon alternatives moves the Scope 3 procurement number meaningfully.
Electricity: switching to a renewable energy tariff (with certificates) can reduce Scope 2 to near zero on a market-based basis.
Commuting: remote and hybrid working cuts commuter emissions, which for some office businesses are the largest single Scope 3 category.

Limitations and next steps

This tool produces a screening estimate suitable for identifying hotspots and setting reduction priorities. A reportable GHG inventory for external disclosure (TCFD, CDP, SECR, CSRD) requires a defined organisational boundary, audited activity data, and a consistent methodology document. Use this output to prioritise data collection, then work with a verified methodology for the final disclosed figure.