How to Calculate Scope 1, 2 and 3 Emissions?

You can’t manage greenhouse gas emissions if you don’t know where they come from. At Zero Emissions Hub, carbon accounting is defined as measuring Scope 1, 2 and 3 emissions and pairing them with action plans for reductions.This article walks through how to calculate each scope in a practical way, using the carbon accounting resources and tools already available on your website — from the Carbon Footprint Calculator to the Methods for Calculating Carbon Emissions – Decision Tree.

What Are Scope 1, 2 and 3 Emissions?

Across your site, carbon accounting is framed in line with the GHG Protocol and ISO 14064 standards:

• Scope 1 – direct emissions from sources you control (e.g. on-site combustion, company vehicles).

• Scope 2 – indirect emissions from purchased electricity, heat or steam.

• Scope 3 – all other relevant value-chain emissions, such as purchased goods and services, business travel, waste, and use of sold products. 

Step 1 – Set Your GHG Boundaries

Before calculating anything, you need to decide what is in and what is out of your inventory. Your article on managing greenhouse gas boundaries (ISO 14064-1) explains why this is essential for a “decision-grade” inventory and for aligning with GHG Protocol scopes. 

Key boundary choices include:

• Organisational boundaries

  • Equity share vs. operational control: which entities do you include?

• Operational boundaries

  • Which sources and sinks are relevant, and which scope do they fall under?

  • How will you treat leased assets, joint ventures, and outsourced operations?

The ISO 14064-1 guidance on your site stresses identifying and documenting all relevant sources and sinks within these boundaries before moving to quantification. 

Step 2 – Calculate Scope 1 Emissions (Direct)

Scope 1 covers direct emissions from sources you own or control, such as:

• Fuel combustion in boilers and generators.

• Company-owned vehicles.

• Process emissions (e.g. industrial processes).

• Fugitive emissions (e.g. refrigerant leaks).

Your Carbon Footprint Calculator shows the core calculation logic clearly:

Emissions = Activity Data × Emission Factor

The calculator multiplies user input (activity) by an emission factor (kg CO₂e per unit of activity) based on reputable datasets.

Practical steps for Scope 1 using your methodology:

1. Collect activity data
   • Fuel use (litres of diesel, litres of petrol, m³ of natural gas).
   • Refrigerant top-ups (kg of gas).
   • Process-related inputs or outputs if relevant.
2. Select the right activity and scope in the calculator
   • Choose Method of Calculation, Sector, Category, Activity, Region and Unit, then set Scope = 1.
3. Apply emission factors
   • The calculator automatically applies relevant emission factors and returns total emissions in kg CO₂e.
4. Review and improve

• Where possible, replace generic factors with organisation- or supplier-specific factors over time, in line with ISO 14064-1. 

Step 3 – Calculate Scope 2 Emissions (Purchased Energy)

Scope 2 focuses on purchased electricity, heat or steam. Your GRI guidance article notes that Scope 2 should distinguish location-based vs market-based results where renewable certificates or green tariffs are used. 

Steps:

1. Gather energy data
   • kWh of electricity, heat or steam for each site or meter.
2. Enter data into the calculator
   • In the Carbon Footprint Calculator, choose the relevant energy activity, set the Region, make sure Scope = 2 and input kWh.
3. Location-based emissions
   • Use the grid average emission factor for the country or region (handled within the tool’s factor library).
4. Market-based emissions (if you buy renewable electricity)

• Where you have contractual instruments (e.g. PPAs, green tariffs), the GRI and GHG Protocol-aligned guidance on your site calls for a separate market-based figure reflecting those purchases.

Step 4 – Calculate Scope 3 Emissions (Value Chain)

Scope 3 typically represents the majority of a company’s footprint and is also the most complex. On your site, SBTi guidance and ESRS material highlight the need for comprehensive Scope 3 coverage, especially for purchased goods and services, business travel, use of sold products and other value-chain categories. 

Your Methods for Calculating Carbon Emissions – Decision Tree is designed exactly for this challenge: it helps organisations choose between spend-based and activity-based approaches for different Scope 3 categories. 

Typical Scope 3 workflow, aligned with your decision tree:

1. Prioritise categories
   • Start with high-impact categories like purchased goods and services, upstream transport, business travel and waste. (The decision tree explicitly asks whether you are planning a medium or high-accuracy Scope 3 inventory for purchased goods and services.) 
2. Choose a calculation method
   • If you only have financial data:
     • Use a spend-based method (emission factors per monetary unit).
   • If you have detailed quantities:
     • Use an activity-based method (e.g. tonne-km for transport, number of hotel nights).
3. Apply the same formula
   • In every case, emissions are calculated as:
     • Emissions = Activity Data × Emission Factor (the same logic used in your Carbon Footprint Calculator). 
4. Use the Scope field correctly
   • When using the calculator, be sure to set Scope = 3 and select the appropriate Category and Activity for each dataset. 
5. Iterate towards higher accuracy

• • Your SBTi guidance stresses that Scope 3 targets should be based on the most relevant categories, with accuracy improving over time as better data become available. 

Step 5 – Use Tools and Frameworks to Improve Data Quality

On your site, you repeatedly connect calculation methods to globally recognised standards:

• GHG Protocol and ISO 14064 as core methodological references. 

• GRI, ISSB, ESRS/CSRD and SBTi for disclosure, structure and target-setting. 

Your Carbon Accounting Decision Tree, Carbon Footprint Calculator and carbon accounting services pages show how these frameworks are translated into practical workflows for companies, cities, government agencies and projects. 

As your GRI guidance notes, calculation approaches should align with GHG Protocol and ISO 14064, ensuring that Scope 2 results can be split into location- and market-based views and that Scope 1 and 3 are captured comprehensively. 

How Zero Emissions Hub Can Support Your Carbon Accounting Journey

The Carbon Accounting & ESG Reporting package services page positions Zero Emissions Hub as an end-to-end partner for GHG accounting: from data collection and methodology selection to reporting, assurance readiness and ongoing monitoring.

Find More Similar Aricles