How to Conduct a Scope 1 Emissions Inventory

For many mid-market companies, Scope 1 emissions are the most tangible part of carbon accounting. They come from assets and activities the company directly owns or controls: fuel burned on-site, company-operated vehicles, process emissions, and refrigerant leaks. That should make them straightforward. In practice, they are often fragmented across facilities, finance systems, fleet logs, maintenance records, and environmental health and safety workflows.

A credible Scope 1 emissions inventory does more than produce a number for an annual report. It creates a repeatable, auditable process for identifying direct emissions sources, assigning ownership, collecting activity data, applying the right calculation methods, and maintaining documentation that stands up to internal review, investor scrutiny, and evolving disclosure expectations.

This guide explains how to conduct a Scope 1 emissions inventory from end to end, with a practical focus on mid-market teams building a process that can scale. If you are still assessing your broader program maturity, start with GreenScore’s free ESG readiness assessment to identify gaps in data, governance, and reporting workflows.

What Scope 1 emissions include

Scope 1 emissions are direct greenhouse gas emissions from sources owned or controlled by your organization. The core reference point is the GHG Protocol, which remains the foundational standard for corporate greenhouse gas accounting.

In most mid-market organizations, Scope 1 emissions typically fall into a few major categories:

• Stationary combustion: natural gas, diesel, propane, fuel oil, or other fuels burned in boilers, furnaces, generators, kilns, or heaters.
• Mobile combustion: gasoline or diesel used by company-owned or company-controlled vehicles, including delivery fleets, service vans, forklifts, and some mobile equipment.
• Fugitive emissions: refrigerant leaks from HVAC and cooling systems, as well as certain emissions from fire suppression or industrial gases.
• Process emissions: emissions released during manufacturing or chemical processes that do not come from fuel combustion.

The key phrase is owned or controlled. If your company leases a facility, outsources logistics, or contracts operations, the treatment may depend on your organizational boundary approach and operational control. That is why the inventory process should begin with boundaries, not calculations.

Why Scope 1 inventories break down

Teams often assume Scope 1 will be the easiest part of the greenhouse gas inventory because data appears operationally close to the business. Yet common issues quickly emerge:

• Facilities teams track fuel use by site, but not in a centralized format.
• Fleet data sits with operations, fuel card vendors, or vehicle leasing providers.
• Refrigerant records are maintained for maintenance compliance, not carbon accounting.
• Entity and site boundaries are not clearly defined after acquisitions or reorganizations.
• Emission factors and global warming potentials are applied inconsistently year to year.
• Documentation is too weak to support assurance or management review.

A reliable inventory requires process discipline. In that sense, Scope 1 accounting is less about complicated math and more about operational coordination, data controls, and consistency.

Step 1: Set organizational and operational boundaries

Before identifying emissions sources, define which legal entities, sites, and operations belong in the inventory. This is especially important for companies with multiple subsidiaries, leased facilities, franchise models, or joint ventures.

Choose a boundary approach

Most companies align to either an equity share approach or a control approach under the GHG Protocol. Mid-market companies usually prefer the control approach because it better matches operational responsibility and internal reporting.

Document:

• Included legal entities
• Included facilities and operating sites
• Treatment of leased assets
• Treatment of joint ventures and minority investments
• Start and end dates for entities acquired or divested during the reporting period

Define what counts as Scope 1

Next, clarify which direct emission categories are relevant to the business. A manufacturer may have stationary combustion, process emissions, and refrigerants. A healthcare company may have generators, vehicle fleets, anesthetic gases, and backup heating systems. A distributor may have mobile combustion and refrigeration units but limited process emissions.

This boundary memo becomes the foundation for inventory consistency year after year and helps avoid disputes later during review.

Step 2: Build a complete source map

Once boundaries are established, create a source map of every potential Scope 1 emissions source across the business. The goal is completeness first, refinement second.

Work through each facility and operating unit with site leaders, facilities managers, fleet managers, EHS, finance, and maintenance personnel. Ask what fuel is consumed on-site, which vehicles are controlled by the company, what gases are refilled or serviced, and whether any production processes emit greenhouse gases directly.

A source map should also identify assets that are not in Scope 1 because they are supplier-operated, landlord-controlled, or otherwise outside your chosen boundary. Exclusions should be explicit, not assumed.

Step 3: Identify data sources and owners

For each emissions source, document the exact system, file, vendor record, or operational log that will supply activity data. Then assign a business owner responsible for submitting or validating it.

At minimum, capture:

• Source name: for example, Dallas Plant Boiler 2 or Northeast Service Fleet.
• Emission category: stationary, mobile, fugitive, or process.
• Activity data type: therms, gallons, liters, kg of refrigerant, etc.
• Data source: utility invoice, AP ledger, fuel card export, maintenance log, SCADA system.
• Data owner: named person or functional team.
• Reporting frequency: monthly, quarterly, annually.
• Evidence retained: invoices, screenshots, service records, engineering notes.

If this step sounds administrative, that is exactly the point. Carbon inventories become dependable when operational responsibility is clear. Many teams benefit from using ESG reporting software to centralize source-level data collection rather than relying on email and spreadsheets.

Step 4: Collect activity data by source type

Scope 1 calculations depend on activity data quality. The better the input, the more defensible the output.

Stationary combustion data

Use actual fuel consumption whenever possible. This may come from vendor invoices, metered usage, fuel delivery records, or internal tank management logs. If you only have spend data, do not convert cost to emissions unless no better option exists and the assumptions are clearly documented.

Important checks include unit consistency, gaps in monthly records, duplicate invoices, and periods that span fiscal year boundaries.

Mobile combustion data

For fleets, fuel consumption data is usually preferable to mileage estimates. Fuel card systems often provide the cleanest record, but telematics, dispatch systems, and vehicle management platforms can help validate anomalies. If using mileage-based estimates, document why fuel data was unavailable and what methodology was used.

Special attention is needed for mixed-use vehicles, leased vehicles under operational control, and non-road equipment such as forklifts or yard tractors.

Fugitive emissions data

Refrigerants are often the most underestimated Scope 1 source because records were designed for maintenance, not emissions accounting. The most practical approach is usually to quantify additions, replacements, and recoveries from service logs, then apply the appropriate gas-specific global warming potential.

Because fugitive emissions can be high impact despite lower volumes, maintain clear equipment-level documentation wherever possible.

Process emissions data

Process emissions require closer collaboration with engineering and EHS teams. Depending on the industry, calculations may rely on mass balance, production throughput, stoichiometric equations, or direct monitoring. If process emissions are relevant to your business, create a technical memo that explains the method in plain language and references the standard used.

If your company is still organizing foundational carbon data, GreenScore’s carbon footprint calculator can help teams structure source-level inputs more consistently.

Step 5: Apply calculation methods and emission factors

Once activity data is collected, convert it into greenhouse gas emissions using appropriate emission factors and global warming potentials. This sounds straightforward, but consistency matters.

Document:

• The calculation method used for each source type
• The emission factor source and version year
• The gases included, such as CO2, CH4, and N2O
• The global warming potential basis used to convert to CO2e
• Any assumptions or estimation methods applied

Align factor selection to recognized standards and your reporting needs. For broader sustainability disclosures, organizations often map their inventory outputs into frameworks such as GRI or the ISSB. The key is not just selecting factors, but preserving a transparent audit trail for why those factors were chosen.

Avoid changing methodologies year to year unless there is a clear reason, such as improved data quality or updated standards. When changes do happen, disclose them internally and assess whether a base-year recalculation is appropriate.

Step 6: Build controls for completeness and accuracy

A Scope 1 inventory is only as strong as the controls behind it. Even before formal assurance, management should be able to answer basic questions: Are all sources included? Who reviewed the data? What evidence supports the final number? How were exceptions handled?

Practical controls include:

• Source completeness check: reconcile site lists against the source map every reporting period.
• Data submission deadlines: set a formal monthly or quarterly close process.
• Variance review: investigate material changes by site, fuel type, or asset class.
• Document retention: keep invoices, logs, and calculation files in a structured repository.
• Change log: track methodology updates, acquisitions, disposals, and corrected errors.
• Reviewer sign-off: assign management review before inventory publication.

This is where software can materially reduce risk. A centralized workflow on the GreenScore platform can help standardize collection, approvals, evidence retention, and reporting outputs across facilities.

Step 7: Handle estimates, gaps, and special cases

No inventory is perfect in its first year. The goal is not perfection at launch; it is disciplined treatment of missing or unusual data.

When estimation is acceptable

Estimation is acceptable when direct data is unavailable, but the method must be reasonable, documented, and consistently applied. For example, you may estimate generator fuel use from run hours and manufacturer fuel consumption rates if invoice data is missing.

Common special cases

• Acquisitions: determine whether newly acquired operations are included for the full year or from the acquisition date.
• Divestitures: remove operations according to your boundary rules and document the timing.
• Shared sites: define whether fuel use is separately metered or allocated by square footage, usage, or contractual responsibility.
• Emergency equipment: backup generators may have low runtime but still belong in the inventory.
• Contractor-operated assets: assess control carefully before including or excluding them.

Strong documentation around estimates matters more than many teams realize. Reviewers generally accept estimates when they are transparent, limited, and supported by logic.

How Scope 1 links to reporting frameworks

Once your Scope 1 inventory is stable, it becomes a building block for multiple disclosure frameworks and stakeholder requests. Investors, customers, lenders, and regulators may all want to see direct emissions data, but the presentation can differ.

For example:

• GRI often emphasizes broad sustainability reporting and management disclosures.
• SASB-aligned reporting may focus on financially material metrics by industry.
• ISSB-related reporting elevates decision-useful sustainability information for capital markets.
• CSRD-related disclosures may require stronger governance, evidence, and cross-functional consistency.

The same underlying inventory should support these outputs with minimal rework. If your team is also preparing narrative disclosures, a structured workflow using a sustainability report generator can help connect emissions data to management commentary and published reports.

A practical Scope 1 inventory checklist

Use this checklist to pressure-test your current process:

1. Define organizational boundaries and document the method used.
2. List all facilities, fleets, and operational sites in scope.
3. Map every potential Scope 1 source by category.
4. Assign a named data owner for each source.
5. Document the primary activity data source and backup source.
6. Collect data in consistent units and reporting periods.
7. Apply approved emission factors and global warming potentials.
8. Review material variances and investigate anomalies.
9. Retain evidence for every material source and estimate.
10. Prepare a short methodology memo for internal and external use.

If you cannot complete several of these steps today, that does not mean the program is failing. It usually means the organization is ready to move from ad hoc carbon tracking to a more mature reporting process.

Practical rule: if a reviewer cannot trace a material Scope 1 number back to its source document, owner, method, and approval, the inventory is not yet fully defensible.

Conclusion

A strong Scope 1 emissions inventory is the operational backbone of carbon reporting. It starts with boundaries, improves through source mapping and owner accountability, and becomes decision-useful when controls and documentation are built into the process. For mid-market companies, the challenge is rarely calculating one emissions figure. The real challenge is creating a repeatable system that can survive growth, audits, investor questions, and changing disclosure expectations.

If you want to see how mature your current process is, take GreenScore’s free ESG readiness assessment. It will help you identify the next steps to strengthen carbon accounting, reporting workflows, and compliance readiness across your ESG program.