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.

Scope 1 / 2 / 3 GHG Emissions Estimator

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.

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 about 0.30 kg CO2e per currency unit, a deliberately rough screening proxy for purchased goods and services.

Tips and example

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: cut Scope 3 first by reducing flights and engaging high-spend suppliers, since direct fuel and energy are usually the smallest slices.