The Complete Guide to Emission Factor Databases: NGA, DEFRA, EPA, IEA, IPCC & Ecoinvent Compared

If you work in carbon accounting, sustainability reporting, or GHG inventory management, you've faced this question: which emission factor database should I be using?

The answer is rarely straightforward. There are at least six major databases in active use globally, each with different geographic coverage, scope, cost, update cycles, and intended purposes. Using the wrong one doesn't just introduce inaccuracy — it can undermine the credibility of your entire disclosure.

This guide provides an independent, practitioner-focused comparison of the six databases you're most likely to encounter: NGA, DEFRA, EPA Hub, IEA, IPCC EFDB, and Ecoinvent. No subscriptions to sell, no platform to push — just a clear breakdown of what each database does well, where it falls short, and when you should reach for it.

Why the choice of database matters

Emission factors are the multipliers that convert your activity data (litres of diesel burned, kilowatt-hours consumed, tonnes of freight moved) into greenhouse gas emissions. The factor you choose directly determines the number that appears in your disclosure.

Here's why database selection is a consequential decision:

• Geographic specificity. An electricity emission factor for Australia (NGA) will differ significantly from one for the UK (DEFRA) or a global average (IEA) — because the generation mix is different. Using a generic factor when a country-specific one exists introduces avoidable error.
• Methodological alignment. Regulatory frameworks often prescribe or recommend specific databases. Australian NGER reporting requires NGA factors. UK Streamlined Energy and Carbon Reporting expects DEFRA. Using a non-aligned database may fail an audit.
• Scope coverage. Some databases excel at Scope 1 and 2 but offer limited Scope 3 factors. Others are purpose-built for lifecycle assessment. Your reporting scope determines which databases are actually useful.
• Cost and accessibility. Four of the six major databases are free. Two require paid licences. For many organisations, cost is a genuine constraint — and using a free database is often perfectly adequate.

Side-by-side comparison

The table above gives you the overview. Below, we go deeper on each database — what it contains, who publishes it, what it's good at, and where its limitations lie.

NGA Factors (Australia)

When to use NGA

• You're reporting under Australia's NGER scheme — NGA factors are legally required
• Your operations are in Australia and you need country-specific factors for stationary combustion, transport fuels, or electricity
• You need state-by-state Australian electricity emission factors (e.g., NSW vs. QLD vs. VIC grid intensities)

Limitations

• Australia-specific only — not applicable for international operations without supplementation
• Scope 3 coverage is narrower than DEFRA (limited upstream/downstream activity categories)
• Published as Excel only — no API, no machine-readable format

DEFRA Conversion Factors (UK)

When to use DEFRA

• You're reporting under UK SECR (Streamlined Energy and Carbon Reporting) or preparing a CDP disclosure
• You need Scope 3 factors for categories like business travel (flights, hotels, rail), freight, waste disposal, water supply, or material use — DEFRA's coverage here is unmatched among free databases
• Your operations span multiple countries and you need a consistent, internationally recognised factor set as your "fallback" source

Limitations

• Electricity factors are UK-specific — for non-UK electricity, you'll need IEA or a national database
• Some factors (particularly for non-UK fuels) are derived from UK-centric assumptions that may not perfectly match local conditions
• Like NGA, published as Excel only

EPA Emission Factor Hub (US)

When to use EPA

• Your operations are in the United States and you need US-specific factors
• You need subregional electricity emission factors (eGRID provides 26 subregion breakdowns across the US)
• You're calculating Scope 3 using spend-based methods — the EPA's USEEIO-derived supply chain factors are the standard reference for US supply chain analysis

Limitations

• US-only — not applicable for international operations
• Scope 3 activity-based factors (flights, hotels, freight) are less comprehensive than DEFRA
• eGRID data typically lags by 1-2 years (2025 release uses 2022 generation data)

IEA Emission Factors (Global)

When to use IEA

• You need electricity emission factors for countries that don't publish their own national factors
• You're building a global Scope 2 inventory and need consistent, comparable factors across all operating countries
• The GHG Protocol or your assurance provider requires IEA as the default source for location-based electricity factors

Limitations

• Paid subscription — a barrier for smaller organisations
• Focused almost exclusively on electricity and heat; does not provide combustion, transport, or Scope 3 factors
• Country-level only — no subnational or grid-region breakdowns (unlike eGRID or NGA state factors)
• Data typically lags by 2 years (e.g., 2025 publication uses 2022 or 2023 energy data)

IPCC Emission Factor Database (Global)

When to use IPCC EFDB

• No country-specific database exists for your operating location
• You need default factors for unusual or niche source categories (e.g., specific industrial processes, agricultural activities, land-use change) not covered by national databases
• You're compiling a national GHG inventory or working on a project that explicitly requires IPCC methodology

Limitations

• Designed for national inventories, not corporate reporting — the factors may not align with corporate GHG Protocol categories
• Tier 1 defaults are deliberately conservative and may overstate or understate emissions compared to country-specific factors
• Not updated on a regular annual cycle — updates are tied to IPCC Guideline revisions, which happen infrequently
• The database interface is functional but dated, and bulk data extraction is not straightforward

Ecoinvent (Global, LCA)

When to use Ecoinvent

• You're conducting a formal Life Cycle Assessment (ISO 14040/14044) or calculating a Product Carbon Footprint
• You need cradle-to-gate emission factors for purchased goods and services (Scope 3, Category 1) that go beyond spend-based estimates
• You're working in an LCA software environment and need integrated, consistent background data

Limitations

• Expensive — the licence fee puts it out of reach for many small and mid-sized organisations
• Complexity — using Ecoinvent properly requires LCA expertise; it's not a simple look-up table
• Not designed for standard corporate GHG reporting — you can't just drop Ecoinvent factors into a Scope 1/2/3 inventory the way you'd use DEFRA or NGA
• Some datasets represent European averages that may not reflect conditions in other regions

Which database should you use?

The decision tree is simpler than it seems. Start with your regulatory context, then consider your geographic scope and reporting needs:

In practice, most practitioners use two or three databases in combination. A typical Australian corporate inventory might use NGA for Scope 1 and 2, DEFRA for Scope 3 business travel and freight, and IEA for electricity at overseas offices. This is normal and expected — no single database covers everything.

The critical thing is to document your sources. For every emission factor in your inventory, record the database name, version, publication year, and the specific table or worksheet reference. This is what auditors check, and it's what gives your disclosure credibility.

Frequently asked questions

Can I mix emission factors from different databases?

Yes — in fact, most practitioners do. The GHG Protocol doesn't require you to use a single source. The key is to use the most appropriate factor for each activity and document your source selection rationale consistently. What you should avoid is switching databases for the same activity between reporting years without a documented reason, as this affects year-on-year comparability.

How often should I update my emission factors?

Best practice is to update annually, when new database versions are published. NGA and DEFRA both publish updated factors each year (typically mid-year), and your reporting should use the most current set available at the time of calculation. When you update, document both the old and new factor values so you can explain year-on-year emission changes that are driven by factor updates rather than operational changes.

What's the difference between location-based and market-based electricity factors?

Location-based factors reflect the average grid emission intensity where your electricity is consumed (e.g., NGA state factors, IEA country factors). Market-based factors reflect the emission intensity of the electricity you've specifically contracted — for example, through renewable energy certificates (RECs), power purchase agreements (PPAs), or green tariffs. The GHG Protocol Scope 2 Guidance requires dual reporting: both location-based and market-based figures if you're making market-based claims.

Are DEFRA factors acceptable for non-UK reporting?

DEFRA factors are widely used internationally, particularly for Scope 3 activities like business travel, freight, and waste. Many CDP disclosures and sustainability reports from non-UK companies cite DEFRA as their source. However, for Scope 1 (fuel combustion) and Scope 2 (electricity), you should prefer your country's national database if one exists — DEFRA's fuel factors assume UK-specific energy content and carbon intensity values.